Hide the buildings











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Shorter version of Skyscrapers Challenge



Task



Given an array of building heights and a positive integer k, find all the permutations(without duplicates) of the heights such that exactly k buildings are visible.



Any building will hide all shorter or equal height buildings behind it.



Any format for input and output is valid.



Input array will never be empty.



In case it is not possible to see exactly as many buildings, output anything that cannot be an answer but no error.



Examples:



(Length of output is shown for very long outputs,but your output should be all possible permutations)



input:[1,2,3,4,5],2
output: 50

input:[5,5,5,5,5,5,5,5],2
output:

input:[1,2,2],2
output:[(1,2,2)]
Seeing from the left, exactly 2 buildings are visible.

input:[1,7,4],2
output:[(4, 7, 1), (1, 7, 4), (4, 1, 7)]

input:[1,2,3,4,5,6,7,8,9],4
output:67284

input:[34,55,11,22],1
output:[(55, 34, 11, 22), (55, 22, 34, 11), (55, 34, 22, 11), (55, 11, 34, 22), (55, 22, 11, 34), (55, 11, 22, 34)]

input:[3,4,1,2,3],2
output:31


This is code-golf so shortest code wins



Optional: If possible, can you add something like if length is greater than 20: print length else print answer. In the footer, not in the code.










share|improve this question
























  • Should the output be all qualifying permutations, or the number thereof?
    – Luis Mendo
    Nov 15 at 6:49










  • It should be all qualifying permutations @LuisMendo
    – Vedant Kandoi
    Nov 15 at 6:54










  • Suggested test case: [1,2,3,4,5],5 -> [(1,2,3,4,5)]. None of the current test cases ensure that answers can support showing all buildings (though I don't know whether any actually have a problem with that).
    – Kamil Drakari
    Nov 15 at 15:27















up vote
15
down vote

favorite
1












Shorter version of Skyscrapers Challenge



Task



Given an array of building heights and a positive integer k, find all the permutations(without duplicates) of the heights such that exactly k buildings are visible.



Any building will hide all shorter or equal height buildings behind it.



Any format for input and output is valid.



Input array will never be empty.



In case it is not possible to see exactly as many buildings, output anything that cannot be an answer but no error.



Examples:



(Length of output is shown for very long outputs,but your output should be all possible permutations)



input:[1,2,3,4,5],2
output: 50

input:[5,5,5,5,5,5,5,5],2
output:

input:[1,2,2],2
output:[(1,2,2)]
Seeing from the left, exactly 2 buildings are visible.

input:[1,7,4],2
output:[(4, 7, 1), (1, 7, 4), (4, 1, 7)]

input:[1,2,3,4,5,6,7,8,9],4
output:67284

input:[34,55,11,22],1
output:[(55, 34, 11, 22), (55, 22, 34, 11), (55, 34, 22, 11), (55, 11, 34, 22), (55, 22, 11, 34), (55, 11, 22, 34)]

input:[3,4,1,2,3],2
output:31


This is code-golf so shortest code wins



Optional: If possible, can you add something like if length is greater than 20: print length else print answer. In the footer, not in the code.










share|improve this question
























  • Should the output be all qualifying permutations, or the number thereof?
    – Luis Mendo
    Nov 15 at 6:49










  • It should be all qualifying permutations @LuisMendo
    – Vedant Kandoi
    Nov 15 at 6:54










  • Suggested test case: [1,2,3,4,5],5 -> [(1,2,3,4,5)]. None of the current test cases ensure that answers can support showing all buildings (though I don't know whether any actually have a problem with that).
    – Kamil Drakari
    Nov 15 at 15:27













up vote
15
down vote

favorite
1









up vote
15
down vote

favorite
1






1





Shorter version of Skyscrapers Challenge



Task



Given an array of building heights and a positive integer k, find all the permutations(without duplicates) of the heights such that exactly k buildings are visible.



Any building will hide all shorter or equal height buildings behind it.



Any format for input and output is valid.



Input array will never be empty.



In case it is not possible to see exactly as many buildings, output anything that cannot be an answer but no error.



Examples:



(Length of output is shown for very long outputs,but your output should be all possible permutations)



input:[1,2,3,4,5],2
output: 50

input:[5,5,5,5,5,5,5,5],2
output:

input:[1,2,2],2
output:[(1,2,2)]
Seeing from the left, exactly 2 buildings are visible.

input:[1,7,4],2
output:[(4, 7, 1), (1, 7, 4), (4, 1, 7)]

input:[1,2,3,4,5,6,7,8,9],4
output:67284

input:[34,55,11,22],1
output:[(55, 34, 11, 22), (55, 22, 34, 11), (55, 34, 22, 11), (55, 11, 34, 22), (55, 22, 11, 34), (55, 11, 22, 34)]

input:[3,4,1,2,3],2
output:31


This is code-golf so shortest code wins



Optional: If possible, can you add something like if length is greater than 20: print length else print answer. In the footer, not in the code.










share|improve this question















Shorter version of Skyscrapers Challenge



Task



Given an array of building heights and a positive integer k, find all the permutations(without duplicates) of the heights such that exactly k buildings are visible.



Any building will hide all shorter or equal height buildings behind it.



Any format for input and output is valid.



Input array will never be empty.



In case it is not possible to see exactly as many buildings, output anything that cannot be an answer but no error.



Examples:



(Length of output is shown for very long outputs,but your output should be all possible permutations)



input:[1,2,3,4,5],2
output: 50

input:[5,5,5,5,5,5,5,5],2
output:

input:[1,2,2],2
output:[(1,2,2)]
Seeing from the left, exactly 2 buildings are visible.

input:[1,7,4],2
output:[(4, 7, 1), (1, 7, 4), (4, 1, 7)]

input:[1,2,3,4,5,6,7,8,9],4
output:67284

input:[34,55,11,22],1
output:[(55, 34, 11, 22), (55, 22, 34, 11), (55, 34, 22, 11), (55, 11, 34, 22), (55, 22, 11, 34), (55, 11, 22, 34)]

input:[3,4,1,2,3],2
output:31


This is code-golf so shortest code wins



Optional: If possible, can you add something like if length is greater than 20: print length else print answer. In the footer, not in the code.







code-golf permutations






share|improve this question















share|improve this question













share|improve this question




share|improve this question








edited Nov 15 at 7:23

























asked Nov 15 at 6:34









Vedant Kandoi

51213




51213












  • Should the output be all qualifying permutations, or the number thereof?
    – Luis Mendo
    Nov 15 at 6:49










  • It should be all qualifying permutations @LuisMendo
    – Vedant Kandoi
    Nov 15 at 6:54










  • Suggested test case: [1,2,3,4,5],5 -> [(1,2,3,4,5)]. None of the current test cases ensure that answers can support showing all buildings (though I don't know whether any actually have a problem with that).
    – Kamil Drakari
    Nov 15 at 15:27


















  • Should the output be all qualifying permutations, or the number thereof?
    – Luis Mendo
    Nov 15 at 6:49










  • It should be all qualifying permutations @LuisMendo
    – Vedant Kandoi
    Nov 15 at 6:54










  • Suggested test case: [1,2,3,4,5],5 -> [(1,2,3,4,5)]. None of the current test cases ensure that answers can support showing all buildings (though I don't know whether any actually have a problem with that).
    – Kamil Drakari
    Nov 15 at 15:27
















Should the output be all qualifying permutations, or the number thereof?
– Luis Mendo
Nov 15 at 6:49




Should the output be all qualifying permutations, or the number thereof?
– Luis Mendo
Nov 15 at 6:49












It should be all qualifying permutations @LuisMendo
– Vedant Kandoi
Nov 15 at 6:54




It should be all qualifying permutations @LuisMendo
– Vedant Kandoi
Nov 15 at 6:54












Suggested test case: [1,2,3,4,5],5 -> [(1,2,3,4,5)]. None of the current test cases ensure that answers can support showing all buildings (though I don't know whether any actually have a problem with that).
– Kamil Drakari
Nov 15 at 15:27




Suggested test case: [1,2,3,4,5],5 -> [(1,2,3,4,5)]. None of the current test cases ensure that answers can support showing all buildings (though I don't know whether any actually have a problem with that).
– Kamil Drakari
Nov 15 at 15:27










9 Answers
9






active

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votes

















up vote
6
down vote














05AB1E, 10 9 bytes



œÙʒη€àÙgQ


Try it online or verify (almost) all test cases (test case [1,2,3,4,5,6,7,8,9],4 times out).

Footer of the TIO does what OP asked at the bottom:




Optional: If possible, can you add something like if length is greater than 20: print length else print answer. In the footer, not in the code.




Explanation:





œ            # Permutations of the (implicit) input-list
# i.e. [1,2,2] → [[1,2,2],[1,2,2],[2,1,2],[2,2,1],[2,1,2],[2,2,1]]
Ù # Only leave the unique permutations
# i.e. [[1,2,2],[1,2,2],[2,1,2],[2,2,1],[2,1,2],[2,2,1]]
# → [[1,2,2],[2,1,2],[2,2,1]]
ʒ # Filter it by:
η # Push the prefixes of the current permutation
# i.e. [1,2,2] → [[1],[1,2],[1,2,2]]
ۈ # Calculate the maximum of each permutation
# i.e. [[1],[1,2],[1,2,2]] → [1,2,2]
Ù # Only leave the unique maximums
# i.e. [1,2,2] → [1,2]
g # And take the length
# i.e. [1,2] → 2
Q # And only leave those equal to the second (implicit) input
# i.e. 2 and 2 → 1 (truthy)





share|improve this answer



















  • 1




    Impressive, every single byte here is part of the function tree!
    – lirtosiast
    Nov 15 at 9:23






  • 1




    @lirtosiast Yeah, 05AB1E has some pretty short builtins sometimes, which were perfect in this challenge. :) It's actually very similar to your Pyth answer I see. Funny thing is, is that the footer for if length is greater than 20: print length; else print answer; is a̶ ̶b̶y̶t̶e̶ ̶l̶o̶n̶g̶e̶r̶ of equal length in comparison to the program itself. xD
    – Kevin Cruijssen
    Nov 15 at 9:25




















up vote
5
down vote














Jelly, 12 10 bytes



Œ!Q»QL=ʋƇ


Try it online!



-2 bytes by @Erik the Outgolfer



This is a dyadic function taking the building heights and k in that order.



Œ!                All permutations of first input
Œ!Q Unique permutations of first input
» Running maximum
Q Unique values
L Length of this array
= Equals k
ʋ Create a monad from these 4 links
»QL=ʋ "Are exactly k buildings visible in arrangement x?"
Ƈ Filter if f(x)
Œ!Q»QL=ʋƇ All distinct perms of first input with k visible buildings.





share|improve this answer



















  • 1




    Hail the new ʋ! (it's pretty older than Ƈ, actually :P)
    – Erik the Outgolfer
    Nov 15 at 12:36




















up vote
4
down vote













Haskell, 73 bytes



import Data.List
f n=filter((n==).length.nub.scanl1 max).nub.permutations


Try it online!






share|improve this answer




























    up vote
    4
    down vote













    Pyth, 18 16 bytes



    fqvzl{meSd._T{.p


    Try it here.



    Note that the online version of the Pyth interpreter throws a memory error on the largest test case.



    f                       Filter lambda T:
    q Are second input and # visible buildings equal?
    v z The second input value
    l { The number of unique elements in
    m the maximums
    e S d ...
    ._ T of prefixes of T
    { .p over unique permutations of (implicit first input)





    share|improve this answer























    • Welcome back! :-)
      – Luis Mendo
      Nov 15 at 12:49


















    up vote
    2
    down vote














    Perl 6, 81 63 bytes



    -18 bytes thanks to nwellnhof!





    {;*.permutations.unique(:with(*eqv*)).grep:{$_==set [max] @_}}


    Try it online!



    Anonymous code block that takes input curried, e.g. f(n)(list). That .unique(:with(*eqv*)) is annoyingly long though :(



    Explanation:



    {;                                                            }  # Anonymous code block
    *.permutations.unique(:with(*eqv*)) # From all distinct permutations
    .grep:{ } # Filter where
    set [max] @_ # Visible buildings
    $_== # Equals num





    share|improve this answer



















    • 1




      FWIW, I just filed a Rakudo issue so we might get rid of that annoying ; eventually ;)
      – nwellnhof
      Nov 15 at 9:55


















    up vote
    2
    down vote














    Japt, 11 bytes



    á f_åÔâ Ê¥V


    Try it online!



    For the longer outputs, adding } l to the end will output the length instead. The online interpreter times out for the [1,2,3,4,5,6,7,8,9],4 test case, regardless of outputting the length or the list.



    Explanation:



    á              :Get all permutations
    f_ :Keep only ones where:
    åÔ : Get the cumulative maximums (i.e. the visible buildings)
    â Ê : Count the number of unique items
    ¥V : True if it's the requested number





    share|improve this answer




























      up vote
      1
      down vote













      JavaScript (ES6), 108 107 bytes



      Takes input as (k)(array). Prints the results with alert().





      k=>P=(a,p=,n=k,h=0)=>a.map((v,i)=>P(a.filter(_=>i--),[...p,v],n-(v>h),v>h?v:h))+a||n||P[p]||alert(P[p]=p)


      Try it online!



      Commented



      k =>                        // k = target number of visible buildings
      P = ( // P = recursive function taking:
      a, // a = list of building heights
      p = , // p = current permutation
      n = k, // n = counter initialized to k
      h = 0 // h = height of the highest building so far
      ) => //
      a.map((v, i) => // for each value v at position i in a:
      P( // do a recursive call:
      a.filter(_ => i--), // using a copy of a without the i-th element
      [...p, v], // append v to p
      n - (v > h), // decrement n if v is greater than h
      v > h ? v : h // update h to max(h, v)
      ) // end of recursive call
      ) // end of map()
      + a || // unless a was not empty,
      n || // or n is not equal to 0,
      P[p] || // or p was already printed,
      alert(P[p] = p) // print p and store it in P





      share|improve this answer






























        up vote
        0
        down vote














        Python 2, 114 113 bytes





        lambda a,n:{p for p in permutations(a)if-~sum(p[i]>max(p[:i])for i in range(1,len(p)))==n}
        from itertools import*


        Try it online!



        -1 byte, thanks to ovs






        Python 3, 113 bytes





        lambda a,n:{p for p in permutations(a)if sum(v>max(p[:p.index(v)]+(v-1,))for v in{*p})==n}
        from itertools import*


        Try it online!






        share|improve this answer






























          up vote
          0
          down vote













          J, 43 38 bytes



          -5 bytes after incorporating an optimization from Kevin's O5AB13 answer



          (]#~[=([:#@~.>./)"1@])[:~.i.@!@#@]A.]


          Try it online!



          ungolfed



          (] #~ [ = ([: #@~. >./)"1@]) ([: ~. i.@!@#@] A. ])


          explanation



          we're merely listing all possible perms i.@!@#@] A. ], taking uniq items thereof with ~., then filtering those by the number of visible building, which must equal the left input.



          the key logic is in the parenthetical verb which calcs the number of visible buildings:



          ([: #@~. >./)


          Here we use a max scan >./ to keep a tally of the tallest building seen so far. Then we just take the unique elements of the max scan, and that's the number of visible buildings.






          share|improve this answer























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            9 Answers
            9






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            9 Answers
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            up vote
            6
            down vote














            05AB1E, 10 9 bytes



            œÙʒη€àÙgQ


            Try it online or verify (almost) all test cases (test case [1,2,3,4,5,6,7,8,9],4 times out).

            Footer of the TIO does what OP asked at the bottom:




            Optional: If possible, can you add something like if length is greater than 20: print length else print answer. In the footer, not in the code.




            Explanation:





            œ            # Permutations of the (implicit) input-list
            # i.e. [1,2,2] → [[1,2,2],[1,2,2],[2,1,2],[2,2,1],[2,1,2],[2,2,1]]
            Ù # Only leave the unique permutations
            # i.e. [[1,2,2],[1,2,2],[2,1,2],[2,2,1],[2,1,2],[2,2,1]]
            # → [[1,2,2],[2,1,2],[2,2,1]]
            ʒ # Filter it by:
            η # Push the prefixes of the current permutation
            # i.e. [1,2,2] → [[1],[1,2],[1,2,2]]
            ۈ # Calculate the maximum of each permutation
            # i.e. [[1],[1,2],[1,2,2]] → [1,2,2]
            Ù # Only leave the unique maximums
            # i.e. [1,2,2] → [1,2]
            g # And take the length
            # i.e. [1,2] → 2
            Q # And only leave those equal to the second (implicit) input
            # i.e. 2 and 2 → 1 (truthy)





            share|improve this answer



















            • 1




              Impressive, every single byte here is part of the function tree!
              – lirtosiast
              Nov 15 at 9:23






            • 1




              @lirtosiast Yeah, 05AB1E has some pretty short builtins sometimes, which were perfect in this challenge. :) It's actually very similar to your Pyth answer I see. Funny thing is, is that the footer for if length is greater than 20: print length; else print answer; is a̶ ̶b̶y̶t̶e̶ ̶l̶o̶n̶g̶e̶r̶ of equal length in comparison to the program itself. xD
              – Kevin Cruijssen
              Nov 15 at 9:25

















            up vote
            6
            down vote














            05AB1E, 10 9 bytes



            œÙʒη€àÙgQ


            Try it online or verify (almost) all test cases (test case [1,2,3,4,5,6,7,8,9],4 times out).

            Footer of the TIO does what OP asked at the bottom:




            Optional: If possible, can you add something like if length is greater than 20: print length else print answer. In the footer, not in the code.




            Explanation:





            œ            # Permutations of the (implicit) input-list
            # i.e. [1,2,2] → [[1,2,2],[1,2,2],[2,1,2],[2,2,1],[2,1,2],[2,2,1]]
            Ù # Only leave the unique permutations
            # i.e. [[1,2,2],[1,2,2],[2,1,2],[2,2,1],[2,1,2],[2,2,1]]
            # → [[1,2,2],[2,1,2],[2,2,1]]
            ʒ # Filter it by:
            η # Push the prefixes of the current permutation
            # i.e. [1,2,2] → [[1],[1,2],[1,2,2]]
            ۈ # Calculate the maximum of each permutation
            # i.e. [[1],[1,2],[1,2,2]] → [1,2,2]
            Ù # Only leave the unique maximums
            # i.e. [1,2,2] → [1,2]
            g # And take the length
            # i.e. [1,2] → 2
            Q # And only leave those equal to the second (implicit) input
            # i.e. 2 and 2 → 1 (truthy)





            share|improve this answer



















            • 1




              Impressive, every single byte here is part of the function tree!
              – lirtosiast
              Nov 15 at 9:23






            • 1




              @lirtosiast Yeah, 05AB1E has some pretty short builtins sometimes, which were perfect in this challenge. :) It's actually very similar to your Pyth answer I see. Funny thing is, is that the footer for if length is greater than 20: print length; else print answer; is a̶ ̶b̶y̶t̶e̶ ̶l̶o̶n̶g̶e̶r̶ of equal length in comparison to the program itself. xD
              – Kevin Cruijssen
              Nov 15 at 9:25















            up vote
            6
            down vote










            up vote
            6
            down vote










            05AB1E, 10 9 bytes



            œÙʒη€àÙgQ


            Try it online or verify (almost) all test cases (test case [1,2,3,4,5,6,7,8,9],4 times out).

            Footer of the TIO does what OP asked at the bottom:




            Optional: If possible, can you add something like if length is greater than 20: print length else print answer. In the footer, not in the code.




            Explanation:





            œ            # Permutations of the (implicit) input-list
            # i.e. [1,2,2] → [[1,2,2],[1,2,2],[2,1,2],[2,2,1],[2,1,2],[2,2,1]]
            Ù # Only leave the unique permutations
            # i.e. [[1,2,2],[1,2,2],[2,1,2],[2,2,1],[2,1,2],[2,2,1]]
            # → [[1,2,2],[2,1,2],[2,2,1]]
            ʒ # Filter it by:
            η # Push the prefixes of the current permutation
            # i.e. [1,2,2] → [[1],[1,2],[1,2,2]]
            ۈ # Calculate the maximum of each permutation
            # i.e. [[1],[1,2],[1,2,2]] → [1,2,2]
            Ù # Only leave the unique maximums
            # i.e. [1,2,2] → [1,2]
            g # And take the length
            # i.e. [1,2] → 2
            Q # And only leave those equal to the second (implicit) input
            # i.e. 2 and 2 → 1 (truthy)





            share|improve this answer















            05AB1E, 10 9 bytes



            œÙʒη€àÙgQ


            Try it online or verify (almost) all test cases (test case [1,2,3,4,5,6,7,8,9],4 times out).

            Footer of the TIO does what OP asked at the bottom:




            Optional: If possible, can you add something like if length is greater than 20: print length else print answer. In the footer, not in the code.




            Explanation:





            œ            # Permutations of the (implicit) input-list
            # i.e. [1,2,2] → [[1,2,2],[1,2,2],[2,1,2],[2,2,1],[2,1,2],[2,2,1]]
            Ù # Only leave the unique permutations
            # i.e. [[1,2,2],[1,2,2],[2,1,2],[2,2,1],[2,1,2],[2,2,1]]
            # → [[1,2,2],[2,1,2],[2,2,1]]
            ʒ # Filter it by:
            η # Push the prefixes of the current permutation
            # i.e. [1,2,2] → [[1],[1,2],[1,2,2]]
            ۈ # Calculate the maximum of each permutation
            # i.e. [[1],[1,2],[1,2,2]] → [1,2,2]
            Ù # Only leave the unique maximums
            # i.e. [1,2,2] → [1,2]
            g # And take the length
            # i.e. [1,2] → 2
            Q # And only leave those equal to the second (implicit) input
            # i.e. 2 and 2 → 1 (truthy)






            share|improve this answer














            share|improve this answer



            share|improve this answer








            edited Nov 15 at 9:27

























            answered Nov 15 at 9:15









            Kevin Cruijssen

            34k554181




            34k554181








            • 1




              Impressive, every single byte here is part of the function tree!
              – lirtosiast
              Nov 15 at 9:23






            • 1




              @lirtosiast Yeah, 05AB1E has some pretty short builtins sometimes, which were perfect in this challenge. :) It's actually very similar to your Pyth answer I see. Funny thing is, is that the footer for if length is greater than 20: print length; else print answer; is a̶ ̶b̶y̶t̶e̶ ̶l̶o̶n̶g̶e̶r̶ of equal length in comparison to the program itself. xD
              – Kevin Cruijssen
              Nov 15 at 9:25
















            • 1




              Impressive, every single byte here is part of the function tree!
              – lirtosiast
              Nov 15 at 9:23






            • 1




              @lirtosiast Yeah, 05AB1E has some pretty short builtins sometimes, which were perfect in this challenge. :) It's actually very similar to your Pyth answer I see. Funny thing is, is that the footer for if length is greater than 20: print length; else print answer; is a̶ ̶b̶y̶t̶e̶ ̶l̶o̶n̶g̶e̶r̶ of equal length in comparison to the program itself. xD
              – Kevin Cruijssen
              Nov 15 at 9:25










            1




            1




            Impressive, every single byte here is part of the function tree!
            – lirtosiast
            Nov 15 at 9:23




            Impressive, every single byte here is part of the function tree!
            – lirtosiast
            Nov 15 at 9:23




            1




            1




            @lirtosiast Yeah, 05AB1E has some pretty short builtins sometimes, which were perfect in this challenge. :) It's actually very similar to your Pyth answer I see. Funny thing is, is that the footer for if length is greater than 20: print length; else print answer; is a̶ ̶b̶y̶t̶e̶ ̶l̶o̶n̶g̶e̶r̶ of equal length in comparison to the program itself. xD
            – Kevin Cruijssen
            Nov 15 at 9:25






            @lirtosiast Yeah, 05AB1E has some pretty short builtins sometimes, which were perfect in this challenge. :) It's actually very similar to your Pyth answer I see. Funny thing is, is that the footer for if length is greater than 20: print length; else print answer; is a̶ ̶b̶y̶t̶e̶ ̶l̶o̶n̶g̶e̶r̶ of equal length in comparison to the program itself. xD
            – Kevin Cruijssen
            Nov 15 at 9:25












            up vote
            5
            down vote














            Jelly, 12 10 bytes



            Œ!Q»QL=ʋƇ


            Try it online!



            -2 bytes by @Erik the Outgolfer



            This is a dyadic function taking the building heights and k in that order.



            Œ!                All permutations of first input
            Œ!Q Unique permutations of first input
            » Running maximum
            Q Unique values
            L Length of this array
            = Equals k
            ʋ Create a monad from these 4 links
            »QL=ʋ "Are exactly k buildings visible in arrangement x?"
            Ƈ Filter if f(x)
            Œ!Q»QL=ʋƇ All distinct perms of first input with k visible buildings.





            share|improve this answer



















            • 1




              Hail the new ʋ! (it's pretty older than Ƈ, actually :P)
              – Erik the Outgolfer
              Nov 15 at 12:36

















            up vote
            5
            down vote














            Jelly, 12 10 bytes



            Œ!Q»QL=ʋƇ


            Try it online!



            -2 bytes by @Erik the Outgolfer



            This is a dyadic function taking the building heights and k in that order.



            Œ!                All permutations of first input
            Œ!Q Unique permutations of first input
            » Running maximum
            Q Unique values
            L Length of this array
            = Equals k
            ʋ Create a monad from these 4 links
            »QL=ʋ "Are exactly k buildings visible in arrangement x?"
            Ƈ Filter if f(x)
            Œ!Q»QL=ʋƇ All distinct perms of first input with k visible buildings.





            share|improve this answer



















            • 1




              Hail the new ʋ! (it's pretty older than Ƈ, actually :P)
              – Erik the Outgolfer
              Nov 15 at 12:36















            up vote
            5
            down vote










            up vote
            5
            down vote










            Jelly, 12 10 bytes



            Œ!Q»QL=ʋƇ


            Try it online!



            -2 bytes by @Erik the Outgolfer



            This is a dyadic function taking the building heights and k in that order.



            Œ!                All permutations of first input
            Œ!Q Unique permutations of first input
            » Running maximum
            Q Unique values
            L Length of this array
            = Equals k
            ʋ Create a monad from these 4 links
            »QL=ʋ "Are exactly k buildings visible in arrangement x?"
            Ƈ Filter if f(x)
            Œ!Q»QL=ʋƇ All distinct perms of first input with k visible buildings.





            share|improve this answer















            Jelly, 12 10 bytes



            Œ!Q»QL=ʋƇ


            Try it online!



            -2 bytes by @Erik the Outgolfer



            This is a dyadic function taking the building heights and k in that order.



            Œ!                All permutations of first input
            Œ!Q Unique permutations of first input
            » Running maximum
            Q Unique values
            L Length of this array
            = Equals k
            ʋ Create a monad from these 4 links
            »QL=ʋ "Are exactly k buildings visible in arrangement x?"
            Ƈ Filter if f(x)
            Œ!Q»QL=ʋƇ All distinct perms of first input with k visible buildings.






            share|improve this answer














            share|improve this answer



            share|improve this answer








            edited Nov 15 at 13:16

























            answered Nov 15 at 8:39









            lirtosiast

            15.3k436104




            15.3k436104








            • 1




              Hail the new ʋ! (it's pretty older than Ƈ, actually :P)
              – Erik the Outgolfer
              Nov 15 at 12:36
















            • 1




              Hail the new ʋ! (it's pretty older than Ƈ, actually :P)
              – Erik the Outgolfer
              Nov 15 at 12:36










            1




            1




            Hail the new ʋ! (it's pretty older than Ƈ, actually :P)
            – Erik the Outgolfer
            Nov 15 at 12:36






            Hail the new ʋ! (it's pretty older than Ƈ, actually :P)
            – Erik the Outgolfer
            Nov 15 at 12:36












            up vote
            4
            down vote













            Haskell, 73 bytes



            import Data.List
            f n=filter((n==).length.nub.scanl1 max).nub.permutations


            Try it online!






            share|improve this answer

























              up vote
              4
              down vote













              Haskell, 73 bytes



              import Data.List
              f n=filter((n==).length.nub.scanl1 max).nub.permutations


              Try it online!






              share|improve this answer























                up vote
                4
                down vote










                up vote
                4
                down vote









                Haskell, 73 bytes



                import Data.List
                f n=filter((n==).length.nub.scanl1 max).nub.permutations


                Try it online!






                share|improve this answer












                Haskell, 73 bytes



                import Data.List
                f n=filter((n==).length.nub.scanl1 max).nub.permutations


                Try it online!







                share|improve this answer












                share|improve this answer



                share|improve this answer










                answered Nov 15 at 7:35









                nimi

                30.8k31985




                30.8k31985






















                    up vote
                    4
                    down vote













                    Pyth, 18 16 bytes



                    fqvzl{meSd._T{.p


                    Try it here.



                    Note that the online version of the Pyth interpreter throws a memory error on the largest test case.



                    f                       Filter lambda T:
                    q Are second input and # visible buildings equal?
                    v z The second input value
                    l { The number of unique elements in
                    m the maximums
                    e S d ...
                    ._ T of prefixes of T
                    { .p over unique permutations of (implicit first input)





                    share|improve this answer























                    • Welcome back! :-)
                      – Luis Mendo
                      Nov 15 at 12:49















                    up vote
                    4
                    down vote













                    Pyth, 18 16 bytes



                    fqvzl{meSd._T{.p


                    Try it here.



                    Note that the online version of the Pyth interpreter throws a memory error on the largest test case.



                    f                       Filter lambda T:
                    q Are second input and # visible buildings equal?
                    v z The second input value
                    l { The number of unique elements in
                    m the maximums
                    e S d ...
                    ._ T of prefixes of T
                    { .p over unique permutations of (implicit first input)





                    share|improve this answer























                    • Welcome back! :-)
                      – Luis Mendo
                      Nov 15 at 12:49













                    up vote
                    4
                    down vote










                    up vote
                    4
                    down vote









                    Pyth, 18 16 bytes



                    fqvzl{meSd._T{.p


                    Try it here.



                    Note that the online version of the Pyth interpreter throws a memory error on the largest test case.



                    f                       Filter lambda T:
                    q Are second input and # visible buildings equal?
                    v z The second input value
                    l { The number of unique elements in
                    m the maximums
                    e S d ...
                    ._ T of prefixes of T
                    { .p over unique permutations of (implicit first input)





                    share|improve this answer














                    Pyth, 18 16 bytes



                    fqvzl{meSd._T{.p


                    Try it here.



                    Note that the online version of the Pyth interpreter throws a memory error on the largest test case.



                    f                       Filter lambda T:
                    q Are second input and # visible buildings equal?
                    v z The second input value
                    l { The number of unique elements in
                    m the maximums
                    e S d ...
                    ._ T of prefixes of T
                    { .p over unique permutations of (implicit first input)






                    share|improve this answer














                    share|improve this answer



                    share|improve this answer








                    edited Nov 15 at 9:01

























                    answered Nov 15 at 6:58









                    lirtosiast

                    15.3k436104




                    15.3k436104












                    • Welcome back! :-)
                      – Luis Mendo
                      Nov 15 at 12:49


















                    • Welcome back! :-)
                      – Luis Mendo
                      Nov 15 at 12:49
















                    Welcome back! :-)
                    – Luis Mendo
                    Nov 15 at 12:49




                    Welcome back! :-)
                    – Luis Mendo
                    Nov 15 at 12:49










                    up vote
                    2
                    down vote














                    Perl 6, 81 63 bytes



                    -18 bytes thanks to nwellnhof!





                    {;*.permutations.unique(:with(*eqv*)).grep:{$_==set [max] @_}}


                    Try it online!



                    Anonymous code block that takes input curried, e.g. f(n)(list). That .unique(:with(*eqv*)) is annoyingly long though :(



                    Explanation:



                    {;                                                            }  # Anonymous code block
                    *.permutations.unique(:with(*eqv*)) # From all distinct permutations
                    .grep:{ } # Filter where
                    set [max] @_ # Visible buildings
                    $_== # Equals num





                    share|improve this answer



















                    • 1




                      FWIW, I just filed a Rakudo issue so we might get rid of that annoying ; eventually ;)
                      – nwellnhof
                      Nov 15 at 9:55















                    up vote
                    2
                    down vote














                    Perl 6, 81 63 bytes



                    -18 bytes thanks to nwellnhof!





                    {;*.permutations.unique(:with(*eqv*)).grep:{$_==set [max] @_}}


                    Try it online!



                    Anonymous code block that takes input curried, e.g. f(n)(list). That .unique(:with(*eqv*)) is annoyingly long though :(



                    Explanation:



                    {;                                                            }  # Anonymous code block
                    *.permutations.unique(:with(*eqv*)) # From all distinct permutations
                    .grep:{ } # Filter where
                    set [max] @_ # Visible buildings
                    $_== # Equals num





                    share|improve this answer



















                    • 1




                      FWIW, I just filed a Rakudo issue so we might get rid of that annoying ; eventually ;)
                      – nwellnhof
                      Nov 15 at 9:55













                    up vote
                    2
                    down vote










                    up vote
                    2
                    down vote










                    Perl 6, 81 63 bytes



                    -18 bytes thanks to nwellnhof!





                    {;*.permutations.unique(:with(*eqv*)).grep:{$_==set [max] @_}}


                    Try it online!



                    Anonymous code block that takes input curried, e.g. f(n)(list). That .unique(:with(*eqv*)) is annoyingly long though :(



                    Explanation:



                    {;                                                            }  # Anonymous code block
                    *.permutations.unique(:with(*eqv*)) # From all distinct permutations
                    .grep:{ } # Filter where
                    set [max] @_ # Visible buildings
                    $_== # Equals num





                    share|improve this answer















                    Perl 6, 81 63 bytes



                    -18 bytes thanks to nwellnhof!





                    {;*.permutations.unique(:with(*eqv*)).grep:{$_==set [max] @_}}


                    Try it online!



                    Anonymous code block that takes input curried, e.g. f(n)(list). That .unique(:with(*eqv*)) is annoyingly long though :(



                    Explanation:



                    {;                                                            }  # Anonymous code block
                    *.permutations.unique(:with(*eqv*)) # From all distinct permutations
                    .grep:{ } # Filter where
                    set [max] @_ # Visible buildings
                    $_== # Equals num






                    share|improve this answer














                    share|improve this answer



                    share|improve this answer








                    edited Nov 15 at 9:49

























                    answered Nov 15 at 7:04









                    Jo King

                    19.1k244102




                    19.1k244102








                    • 1




                      FWIW, I just filed a Rakudo issue so we might get rid of that annoying ; eventually ;)
                      – nwellnhof
                      Nov 15 at 9:55














                    • 1




                      FWIW, I just filed a Rakudo issue so we might get rid of that annoying ; eventually ;)
                      – nwellnhof
                      Nov 15 at 9:55








                    1




                    1




                    FWIW, I just filed a Rakudo issue so we might get rid of that annoying ; eventually ;)
                    – nwellnhof
                    Nov 15 at 9:55




                    FWIW, I just filed a Rakudo issue so we might get rid of that annoying ; eventually ;)
                    – nwellnhof
                    Nov 15 at 9:55










                    up vote
                    2
                    down vote














                    Japt, 11 bytes



                    á f_åÔâ Ê¥V


                    Try it online!



                    For the longer outputs, adding } l to the end will output the length instead. The online interpreter times out for the [1,2,3,4,5,6,7,8,9],4 test case, regardless of outputting the length or the list.



                    Explanation:



                    á              :Get all permutations
                    f_ :Keep only ones where:
                    åÔ : Get the cumulative maximums (i.e. the visible buildings)
                    â Ê : Count the number of unique items
                    ¥V : True if it's the requested number





                    share|improve this answer

























                      up vote
                      2
                      down vote














                      Japt, 11 bytes



                      á f_åÔâ Ê¥V


                      Try it online!



                      For the longer outputs, adding } l to the end will output the length instead. The online interpreter times out for the [1,2,3,4,5,6,7,8,9],4 test case, regardless of outputting the length or the list.



                      Explanation:



                      á              :Get all permutations
                      f_ :Keep only ones where:
                      åÔ : Get the cumulative maximums (i.e. the visible buildings)
                      â Ê : Count the number of unique items
                      ¥V : True if it's the requested number





                      share|improve this answer























                        up vote
                        2
                        down vote










                        up vote
                        2
                        down vote










                        Japt, 11 bytes



                        á f_åÔâ Ê¥V


                        Try it online!



                        For the longer outputs, adding } l to the end will output the length instead. The online interpreter times out for the [1,2,3,4,5,6,7,8,9],4 test case, regardless of outputting the length or the list.



                        Explanation:



                        á              :Get all permutations
                        f_ :Keep only ones where:
                        åÔ : Get the cumulative maximums (i.e. the visible buildings)
                        â Ê : Count the number of unique items
                        ¥V : True if it's the requested number





                        share|improve this answer













                        Japt, 11 bytes



                        á f_åÔâ Ê¥V


                        Try it online!



                        For the longer outputs, adding } l to the end will output the length instead. The online interpreter times out for the [1,2,3,4,5,6,7,8,9],4 test case, regardless of outputting the length or the list.



                        Explanation:



                        á              :Get all permutations
                        f_ :Keep only ones where:
                        åÔ : Get the cumulative maximums (i.e. the visible buildings)
                        â Ê : Count the number of unique items
                        ¥V : True if it's the requested number






                        share|improve this answer












                        share|improve this answer



                        share|improve this answer










                        answered Nov 15 at 15:27









                        Kamil Drakari

                        2,551416




                        2,551416






















                            up vote
                            1
                            down vote













                            JavaScript (ES6), 108 107 bytes



                            Takes input as (k)(array). Prints the results with alert().





                            k=>P=(a,p=,n=k,h=0)=>a.map((v,i)=>P(a.filter(_=>i--),[...p,v],n-(v>h),v>h?v:h))+a||n||P[p]||alert(P[p]=p)


                            Try it online!



                            Commented



                            k =>                        // k = target number of visible buildings
                            P = ( // P = recursive function taking:
                            a, // a = list of building heights
                            p = , // p = current permutation
                            n = k, // n = counter initialized to k
                            h = 0 // h = height of the highest building so far
                            ) => //
                            a.map((v, i) => // for each value v at position i in a:
                            P( // do a recursive call:
                            a.filter(_ => i--), // using a copy of a without the i-th element
                            [...p, v], // append v to p
                            n - (v > h), // decrement n if v is greater than h
                            v > h ? v : h // update h to max(h, v)
                            ) // end of recursive call
                            ) // end of map()
                            + a || // unless a was not empty,
                            n || // or n is not equal to 0,
                            P[p] || // or p was already printed,
                            alert(P[p] = p) // print p and store it in P





                            share|improve this answer



























                              up vote
                              1
                              down vote













                              JavaScript (ES6), 108 107 bytes



                              Takes input as (k)(array). Prints the results with alert().





                              k=>P=(a,p=,n=k,h=0)=>a.map((v,i)=>P(a.filter(_=>i--),[...p,v],n-(v>h),v>h?v:h))+a||n||P[p]||alert(P[p]=p)


                              Try it online!



                              Commented



                              k =>                        // k = target number of visible buildings
                              P = ( // P = recursive function taking:
                              a, // a = list of building heights
                              p = , // p = current permutation
                              n = k, // n = counter initialized to k
                              h = 0 // h = height of the highest building so far
                              ) => //
                              a.map((v, i) => // for each value v at position i in a:
                              P( // do a recursive call:
                              a.filter(_ => i--), // using a copy of a without the i-th element
                              [...p, v], // append v to p
                              n - (v > h), // decrement n if v is greater than h
                              v > h ? v : h // update h to max(h, v)
                              ) // end of recursive call
                              ) // end of map()
                              + a || // unless a was not empty,
                              n || // or n is not equal to 0,
                              P[p] || // or p was already printed,
                              alert(P[p] = p) // print p and store it in P





                              share|improve this answer

























                                up vote
                                1
                                down vote










                                up vote
                                1
                                down vote









                                JavaScript (ES6), 108 107 bytes



                                Takes input as (k)(array). Prints the results with alert().





                                k=>P=(a,p=,n=k,h=0)=>a.map((v,i)=>P(a.filter(_=>i--),[...p,v],n-(v>h),v>h?v:h))+a||n||P[p]||alert(P[p]=p)


                                Try it online!



                                Commented



                                k =>                        // k = target number of visible buildings
                                P = ( // P = recursive function taking:
                                a, // a = list of building heights
                                p = , // p = current permutation
                                n = k, // n = counter initialized to k
                                h = 0 // h = height of the highest building so far
                                ) => //
                                a.map((v, i) => // for each value v at position i in a:
                                P( // do a recursive call:
                                a.filter(_ => i--), // using a copy of a without the i-th element
                                [...p, v], // append v to p
                                n - (v > h), // decrement n if v is greater than h
                                v > h ? v : h // update h to max(h, v)
                                ) // end of recursive call
                                ) // end of map()
                                + a || // unless a was not empty,
                                n || // or n is not equal to 0,
                                P[p] || // or p was already printed,
                                alert(P[p] = p) // print p and store it in P





                                share|improve this answer














                                JavaScript (ES6), 108 107 bytes



                                Takes input as (k)(array). Prints the results with alert().





                                k=>P=(a,p=,n=k,h=0)=>a.map((v,i)=>P(a.filter(_=>i--),[...p,v],n-(v>h),v>h?v:h))+a||n||P[p]||alert(P[p]=p)


                                Try it online!



                                Commented



                                k =>                        // k = target number of visible buildings
                                P = ( // P = recursive function taking:
                                a, // a = list of building heights
                                p = , // p = current permutation
                                n = k, // n = counter initialized to k
                                h = 0 // h = height of the highest building so far
                                ) => //
                                a.map((v, i) => // for each value v at position i in a:
                                P( // do a recursive call:
                                a.filter(_ => i--), // using a copy of a without the i-th element
                                [...p, v], // append v to p
                                n - (v > h), // decrement n if v is greater than h
                                v > h ? v : h // update h to max(h, v)
                                ) // end of recursive call
                                ) // end of map()
                                + a || // unless a was not empty,
                                n || // or n is not equal to 0,
                                P[p] || // or p was already printed,
                                alert(P[p] = p) // print p and store it in P






                                share|improve this answer














                                share|improve this answer



                                share|improve this answer








                                edited Nov 15 at 10:46

























                                answered Nov 15 at 10:04









                                Arnauld

                                68.9k584289




                                68.9k584289






















                                    up vote
                                    0
                                    down vote














                                    Python 2, 114 113 bytes





                                    lambda a,n:{p for p in permutations(a)if-~sum(p[i]>max(p[:i])for i in range(1,len(p)))==n}
                                    from itertools import*


                                    Try it online!



                                    -1 byte, thanks to ovs






                                    Python 3, 113 bytes





                                    lambda a,n:{p for p in permutations(a)if sum(v>max(p[:p.index(v)]+(v-1,))for v in{*p})==n}
                                    from itertools import*


                                    Try it online!






                                    share|improve this answer



























                                      up vote
                                      0
                                      down vote














                                      Python 2, 114 113 bytes





                                      lambda a,n:{p for p in permutations(a)if-~sum(p[i]>max(p[:i])for i in range(1,len(p)))==n}
                                      from itertools import*


                                      Try it online!



                                      -1 byte, thanks to ovs






                                      Python 3, 113 bytes





                                      lambda a,n:{p for p in permutations(a)if sum(v>max(p[:p.index(v)]+(v-1,))for v in{*p})==n}
                                      from itertools import*


                                      Try it online!






                                      share|improve this answer

























                                        up vote
                                        0
                                        down vote










                                        up vote
                                        0
                                        down vote










                                        Python 2, 114 113 bytes





                                        lambda a,n:{p for p in permutations(a)if-~sum(p[i]>max(p[:i])for i in range(1,len(p)))==n}
                                        from itertools import*


                                        Try it online!



                                        -1 byte, thanks to ovs






                                        Python 3, 113 bytes





                                        lambda a,n:{p for p in permutations(a)if sum(v>max(p[:p.index(v)]+(v-1,))for v in{*p})==n}
                                        from itertools import*


                                        Try it online!






                                        share|improve this answer















                                        Python 2, 114 113 bytes





                                        lambda a,n:{p for p in permutations(a)if-~sum(p[i]>max(p[:i])for i in range(1,len(p)))==n}
                                        from itertools import*


                                        Try it online!



                                        -1 byte, thanks to ovs






                                        Python 3, 113 bytes





                                        lambda a,n:{p for p in permutations(a)if sum(v>max(p[:p.index(v)]+(v-1,))for v in{*p})==n}
                                        from itertools import*


                                        Try it online!







                                        share|improve this answer














                                        share|improve this answer



                                        share|improve this answer








                                        edited Nov 15 at 10:22

























                                        answered Nov 15 at 7:57









                                        TFeld

                                        13.5k21139




                                        13.5k21139






















                                            up vote
                                            0
                                            down vote













                                            J, 43 38 bytes



                                            -5 bytes after incorporating an optimization from Kevin's O5AB13 answer



                                            (]#~[=([:#@~.>./)"1@])[:~.i.@!@#@]A.]


                                            Try it online!



                                            ungolfed



                                            (] #~ [ = ([: #@~. >./)"1@]) ([: ~. i.@!@#@] A. ])


                                            explanation



                                            we're merely listing all possible perms i.@!@#@] A. ], taking uniq items thereof with ~., then filtering those by the number of visible building, which must equal the left input.



                                            the key logic is in the parenthetical verb which calcs the number of visible buildings:



                                            ([: #@~. >./)


                                            Here we use a max scan >./ to keep a tally of the tallest building seen so far. Then we just take the unique elements of the max scan, and that's the number of visible buildings.






                                            share|improve this answer



























                                              up vote
                                              0
                                              down vote













                                              J, 43 38 bytes



                                              -5 bytes after incorporating an optimization from Kevin's O5AB13 answer



                                              (]#~[=([:#@~.>./)"1@])[:~.i.@!@#@]A.]


                                              Try it online!



                                              ungolfed



                                              (] #~ [ = ([: #@~. >./)"1@]) ([: ~. i.@!@#@] A. ])


                                              explanation



                                              we're merely listing all possible perms i.@!@#@] A. ], taking uniq items thereof with ~., then filtering those by the number of visible building, which must equal the left input.



                                              the key logic is in the parenthetical verb which calcs the number of visible buildings:



                                              ([: #@~. >./)


                                              Here we use a max scan >./ to keep a tally of the tallest building seen so far. Then we just take the unique elements of the max scan, and that's the number of visible buildings.






                                              share|improve this answer

























                                                up vote
                                                0
                                                down vote










                                                up vote
                                                0
                                                down vote









                                                J, 43 38 bytes



                                                -5 bytes after incorporating an optimization from Kevin's O5AB13 answer



                                                (]#~[=([:#@~.>./)"1@])[:~.i.@!@#@]A.]


                                                Try it online!



                                                ungolfed



                                                (] #~ [ = ([: #@~. >./)"1@]) ([: ~. i.@!@#@] A. ])


                                                explanation



                                                we're merely listing all possible perms i.@!@#@] A. ], taking uniq items thereof with ~., then filtering those by the number of visible building, which must equal the left input.



                                                the key logic is in the parenthetical verb which calcs the number of visible buildings:



                                                ([: #@~. >./)


                                                Here we use a max scan >./ to keep a tally of the tallest building seen so far. Then we just take the unique elements of the max scan, and that's the number of visible buildings.






                                                share|improve this answer














                                                J, 43 38 bytes



                                                -5 bytes after incorporating an optimization from Kevin's O5AB13 answer



                                                (]#~[=([:#@~.>./)"1@])[:~.i.@!@#@]A.]


                                                Try it online!



                                                ungolfed



                                                (] #~ [ = ([: #@~. >./)"1@]) ([: ~. i.@!@#@] A. ])


                                                explanation



                                                we're merely listing all possible perms i.@!@#@] A. ], taking uniq items thereof with ~., then filtering those by the number of visible building, which must equal the left input.



                                                the key logic is in the parenthetical verb which calcs the number of visible buildings:



                                                ([: #@~. >./)


                                                Here we use a max scan >./ to keep a tally of the tallest building seen so far. Then we just take the unique elements of the max scan, and that's the number of visible buildings.







                                                share|improve this answer














                                                share|improve this answer



                                                share|improve this answer








                                                edited 2 days ago

























                                                answered 2 days ago









                                                Jonah

                                                1,921816




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