Count Up, Replace, Repeat!

Question

Definition

Define the n^th array of the CURR sequence as follows.

1. Begin with the singleton array A = [n].

2. For each integer k in A, replace the entry k with k natural numbers, counting up from 1 to k.

3. Repeat the previous step n - 1 more times.

For example, if n = 3, we start with the array [3].

We replace 3 with 1, 2, 3, yielding [1, 2, 3].

We now replace 1, 2, and 3 with 1; 1, 2 and 1, 2, 3 (resp.), yielding [1, 1, 2, 1, 2, 3].

Finally, we perform the same replacements as in the previous step for all six integers in the array, yielding [1, 1, 1, 2, 1, 1, 2, 1, 2, 3]. This is the third CURR array.

Task

Write a program of a function that, given a strictly positive integer n as input, computes the n^th CURR array.

The output has to be a flat list of some kind (and array returned from a function, a string representation of your language's array syntax, whitespace-separated, etc.).

This is code-golf. May the shortest code in bytes win!

Test cases

 1 -> [1]
 2 -> [1, 1, 2]
 3 -> [1, 1, 1, 2, 1, 1, 2, 1, 2, 3]
 4 -> [1, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 2, 1, 2, 3, 1, 1, 1, 2, 1, 1, 2, 1, 2, 3, 1, 1, 2, 1, 2, 3, 1, 2, 3, 4]
 5 -> [1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 2, 1, 2, 3, 1, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 2, 1, 2, 3, 1, 1, 1, 2, 1, 1, 2, 1, 2, 3, 1, 1, 2, 1, 2, 3, 1, 2, 3, 4, 1, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 2, 1, 2, 3, 1, 1, 1, 2, 1, 1, 2, 1, 2, 3, 1, 1, 2, 1, 2, 3, 1, 2, 3, 4, 1, 1, 1, 2, 1, 1, 2, 1, 2, 3, 1, 1, 2, 1, 2, 3, 1, 2, 3, 4, 1, 1, 2, 1, 2, 3, 1, 2, 3, 4, 1, 2, 3, 4, 5]
 6 -> [1, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 2, 1, 2, 3, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 2, 1, 2, 3, 1, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 2, 1, 2, 3, 1, 1, 1, 2, 1, 1, 2, 1, 2, 3, 1, 1, 2, 1, 2, 3, 1, 2, 3, 4, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 2, 1, 2, 3, 1, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 2, 1, 2, 3, 1, 1, 1, 2, 1, 1, 2, 1, 2, 3, 1, 1, 2, 1, 2, 3, 1, 2, 3, 4, 1, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 2, 1, 2, 3, 1, 1, 1, 2, 1, 1, 2, 1, 2, 3, 1, 1, 2, 1, 2, 3, 1, 2, 3, 4, 1, 1, 1, 2, 1, 1, 2, 1, 2, 3, 1, 1, 2, 1, 2, 3, 1, 2, 3, 4, 1, 1, 2, 1, 2, 3, 1, 2, 3, 4, 1, 2, 3, 4, 5, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 2, 1, 2, 3, 1, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 2, 1, 2, 3, 1, 1, 1, 2, 1, 1, 2, 1, 2, 3, 1, 1, 2, 1, 2, 3, 1, 2, 3, 4, 1, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 2, 1, 2, 3, 1, 1, 1, 2, 1, 1, 2, 1, 2, 3, 1, 1, 2, 1, 2, 3, 1, 2, 3, 4, 1, 1, 1, 2, 1, 1, 2, 1, 2, 3, 1, 1, 2, 1, 2, 3, 1, 2, 3, 4, 1, 1, 2, 1, 2, 3, 1, 2, 3, 4, 1, 2, 3, 4, 5, 1, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 2, 1, 2, 3, 1, 1, 1, 2, 1, 1, 2, 1, 2, 3, 1, 1, 2, 1, 2, 3, 1, 2, 3, 4, 1, 1, 1, 2, 1, 1, 2, 1, 2, 3, 1, 1, 2, 1, 2, 3, 1, 2, 3, 4, 1, 1, 2, 1, 2, 3, 1, 2, 3, 4, 1, 2, 3, 4, 5, 1, 1, 1, 2, 1, 1, 2, 1, 2, 3, 1, 1, 2, 1, 2, 3, 1, 2, 3, 4, 1, 1, 2, 1, 2, 3, 1, 2, 3, 4, 1, 2, 3, 4, 5, 1, 1, 2, 1, 2, 3, 1, 2, 3, 4, 1, 2, 3, 4, 5, 1, 2, 3, 4, 5, 6]

Answer 1

Jelly, 3 bytes

R¡F

Try it online

Explanation

R¡F    Argument n

R      Yield range [1..n]
 ¡     Repeat n times
  F    Flatten the result

Answer 2

Python, 50 bytes

lambda i:eval("[i "+"for i in range(1,i+1)"*i+"]")

Scope abuse! For example, for i=3, the string to be evaluated expands to.

[i for i in range(1,i+1)for i in range(1,i+1)for i in range(1,i+1)]

Somehow, despite using the function input variable i for everything, Python distinguishes each iteration index as belonging to a separate scope as if the expression were

[l for j in range(1,i+1)for k in range(1,j+1)for l in range(1,k+1)]

with i the input to the function.

Answer 3

05AB1E, 6 3 bytes

DFL

Explained

D     # duplicate input
 F    # input times do
  L   # range(1,N)

Try it online

Saved 3 bytes thanks to @Adnan

Answer 4

Retina, 33 bytes

$
$.`$*0
+%(M!&`1.*(?=0)|^.+
O`.+

Input and output in unary.

Try it online!

Even though I didn't use the closed form for the related challenge, adapting this answer was surprisingly tricky.

Answer 5

Python 2, 82 bytes

lambda n:[1+bin(i)[::-1].find('1')for i in range(1<<2*n-1)if bin(i).count('1')==n]

This isn't the shortest solution, but it illustrates an interesting method:

• Write down the first 2^(2*n-1) numbers in binary
• Keep those with exactly n ones
• For each number, count the number of trailing zeroes, and add 1.

Answer 6

Actually, 9 bytes

;#@`♂RΣ`n

Try it online!

Explanation:

;#@`♂RΣ`n
;#@        dupe n, make a singleton list, swap with n
   `♂RΣ`n  call the following function n times:
    ♂R       range(1, k+1) for k in list
      Σ      concatenate the ranges

Thanks to Leaky Nun for a byte, and inspiration for another 2 bytes.

Answer 7

C#, 128 Bytes

List<int>j(int n){var l=new List<int>(){n};for(;n>0;n--)l=l.Select(p=>Enumerable.Range(1,p)).SelectMany(m=>m).ToList();return l;

Answer 8

APL, 11 bytes

{∊⍳¨∘∊⍣⍵+⍵}

Test:

      {∊⍳¨∘∊⍣⍵+⍵} 3
1 1 1 2 1 1 2 1 2 3

Explanation:

• +⍵: starting with ⍵,
• ⍣⍵: do the following ⍵ times:
  • ⍳¨∘∊: flatten the input, and then generate a list [1..N] for each N in the input
• ∊: flatten the result of that

Answer 9

CJam, 14 bytes

{_a\{:,:~:)}*}

Test it here.

Explanation

_a   e# Duplicate N and wrap it in an array.
\    e# Swap with other copy of N.
{    e# Do this N times...
  :, e#   Turn each x into [0 1 ... x-1].
  :~ e#   Unwrap each of those arrays.
  :) e#   Increment each element.
}*

Answer 10

Haskell, 33 bytes

f n=iterate(>>= \a->[1..a])[n]!!n

Thanks to nimi for saving a byte.

A pointfree version is longer (35 bytes):

(!!)=<<iterate(>>= \a->[1..a]).pure

Answer 11

Mathematica, 27 26 bytes

1 byte saved with some inspiration from Essari's answer.

Flatten@Nest[Range,{#},#]&

Fairly straightforward: for input x we start with {x} and then apply the Range to it x times (Range is Listable which means that it automatically applies to the integers inside arbitrarily nested lists). At the end Flatten the result.

Answer 12

Python 3, 75 74 bytes

def f(k):N=[k];exec('A=N;N=[]\nfor i in A:N+=range(1,i+1)\n'*k+'print(N)')

This is just a straightforward translation of the problem description to code.

Edit: Saved one byte thanks to @Dennis.

Answer 13

JavaScript (Firefox 30-57), 63 60 bytes

f=n=>eval(`[${`for(n of Array(n+1).keys())`.repeat(n--)}n+1]`)

Port of @xnor's Python answer.

Answer 14

R, 60 49 bytes

Pretty straightforward use of unlist and sapply.

y=x=scan();for(i in 1:x)y=unlist(sapply(y,seq));y

Thanks to @MickyT for saving 11 bytes

Answer 15

Clojure, 59 bytes

(fn[n](nth(iterate #(mapcat(fn[x](range 1(inc x)))%)[n])n))

Explanation:

Really straight forward way to solve the problem. Working from the inside out:

(1) (fn[x](range 1(inc x))) ;; return a list from 1 to x
(2) #(mapcat (1) %)         ;; map (1) over each item in list and flatten result
(3) (iterate (2) [n])       ;; call (2) repeatedly e.g. (f (f (f [n])))
(4) (nth (3) n))            ;; return the nth value of the iteration

Answer 16

php 121

Not really very much in the way of tricks behind this one. Flattening an array in php isn't short so it's necessary to build it flat in the first place

<?php for($a=[$b=$argv[1]];$b--;)$a=array_reduce($a,function($r,$v){return array_merge($r,range(1,$v));},[]);print_r($a);

Answer 17

Pyth, 8 bytes

usSMGQ]Q

Try it online!

usSMGQ]Q   input as Q

u    Q     repeat for Q times,
      ]Q   starting as [Q]:

  SMG          convert each number in the array to its range
 s             flatten

           then implicitly prints the result.

Answer 18

Jelly, 7 bytes

Quick, before Dennis answers (jk)

WR€F$³¡

Try it online!

WR€F$³¡  Main monadic chain. Argument: z

W        Yield [z].
     ³¡  Repeat the following z times:
 R€          Convert each number in the array to the corresponding range.
   F         Flatten the array.

Answer 19

J, 18 bytes

([:;<@(1+i.)"0)^:]

Straight-forward approach based on the process described in the challenge.

Usage

   f =: ([:;<@(1+i.)"0)^:]
   f 1
1
   f 2
1 1 2
   f 3
1 1 1 2 1 1 2 1 2 3
   f 4
1 1 1 1 2 1 1 1 2 1 1 2 1 2 3 1 1 1 2 1 1 2 1 2 3 1 1 2 1 2 3 1 2 3 4

Explanation

([:;<@(1+i.)"0)^:]  Input: n
                 ]  Identity function, gets the value n
(     ...     )^:   Repeat the following n times with an initial value [n]
      (    )"0        Means rank 0, or to operate on each atom in the list
         i.           Create a range from 0 to that value, exclusive
       1+             Add 1 to each to make the range from 1 to that value
    <@                Box the value
 [:;                  Combine the boxes and unbox them to make a list and return
                    Return the final result after n iterations

Answer 20

Python 2, 69 68 66 bytes

def f(n):a=[n];exec'a=sum([range(1,i+1)for i in a],[]);'*n;print a

Edit: Saved 1 byte thanks to @xnor. Saved 2 bytes thanks to @Dennis♦.

Answer 21

F# , 63 bytes

fun n->Seq.fold(fun A _->List.collect(fun k->[1..k])A)[n]{1..n}

Returns an anonymous function taking n as input.

Replaces every entry k in A with [1..k], repeats the process n times, starting with A = [n].

Answer 22

Swift 3, 58 Bytes

Meant to run directly in the a playground, with n set to the input:

var x=[n];for i in 0..<n{x=x.reduce([]){$0+[Int](1...$1)}}

Ungolfed, with most short hand notation reverted:

let n = 3 //input

var x: Array<Int> = [n]
for i in 0..<n {
    x = x.reduce(Array<Int>[], combine: { accumulator, element in
        accumulator + Array<Int>(1...element)
    })
}

Answer 23

Java, 159 Bytes

Procedure

int[] q(int y){int z[]=new int[]{y};for(int i=0;i<y;i++){int d=0,a=0;for(int c:z)d+=c;int[]r=new int[d];for(int c:z)for(int j=0;j<c;)r[a++]=++j;z=r;}return z;}

Usage

public static void main(String[] args){String out = "["; int [] b = q(6);for(int c:b)out+=c+", ";System.out.println(out+"]");}

public static int[] q(int y){int z[]=new int[]{y};for(int i=0;i<y;i++){int d=0,a=0;for(int c:z)d+=c;int[]r=new int[d];for(int c:z)for(int j=0;j<c;)r[a++]=++j;z=r;}return z;}

Sample output:

[1, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 2, 1, 2, 3, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 2, 1, 2, 3, 1, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 2, 1, 2, 3, 1, 1, 1, 2, 1, 1, 2, 1, 2, 3, 1, 1, 2, 1, 2, 3, 1, 2, 3, 4, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 2, 1, 2, 3, 1, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 2, 1, 2, 3, 1, 1, 1, 2, 1, 1, 2, 1, 2, 3, 1, 1, 2, 1, 2, 3, 1, 2, 3, 4, 1, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 2, 1, 2, 3, 1, 1, 1, 2, 1, 1, 2, 1, 2, 3, 1, 1, 2, 1, 2, 3, 1, 2, 3, 4, 1, 1, 1, 2, 1, 1, 2, 1, 2, 3, 1, 1, 2, 1, 2, 3, 1, 2, 3, 4, 1, 1, 2, 1, 2, 3, 1, 2, 3, 4, 1, 2, 3, 4, 5, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 2, 1, 2, 3, 1, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 2, 1, 2, 3, 1, 1, 1, 2, 1, 1, 2, 1, 2, 3, 1, 1, 2, 1, 2, 3, 1, 2, 3, 4, 1, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 2, 1, 2, 3, 1, 1, 1, 2, 1, 1, 2, 1, 2, 3, 1, 1, 2, 1, 2, 3, 1, 2, 3, 4, 1, 1, 1, 2, 1, 1, 2, 1, 2, 3, 1, 1, 2, 1, 2, 3, 1, 2, 3, 4, 1, 1, 2, 1, 2, 3, 1, 2, 3, 4, 1, 2, 3, 4, 5, 1, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 2, 1, 2, 3, 1, 1, 1, 2, 1, 1, 2, 1, 2, 3, 1, 1, 2, 1, 2, 3, 1, 2, 3, 4, 1, 1, 1, 2, 1, 1, 2, 1, 2, 3, 1, 1, 2, 1, 2, 3, 1, 2, 3, 4, 1, 1, 2, 1, 2, 3, 1, 2, 3, 4, 1, 2, 3, 4, 5, 1, 1, 1, 2, 1, 1, 2, 1, 2, 3, 1, 1, 2, 1, 2, 3, 1, 2, 3, 4, 1, 1, 2, 1, 2, 3, 1, 2, 3, 4, 1, 2, 3, 4, 5, 1, 1, 2, 1, 2, 3, 1, 2, 3, 4, 1, 2, 3, 4, 5, 1, 2, 3, 4, 5, 6, ]

Answer 24

Bash + GNU utilities, 49

• 1 byte saved thanks to @Dennis.

Piped recursive functions FTW!

f()((($1))&&xargs -l seq|f $[$1-1]||dd)
f $1<<<$1

n is passed on the command-line. Output is newline-separated.

The use of dd causes statistics to be sent to STDERR. I think this is OK, but if not, dd can be replaced with cat at a cost of 1 extra byte.

Answer 25

PHP, 100 98 bytes

Run with php -r '<code>' <n>.

for($a=[$n=$argv[1]];$n--;$a=$b)for($b=[],$k=0;$c=$a[$k++];)for($i=0;$i++<$c;)$b[]=$i;print_r($a);

In each iteration create a temporary copy looping from 1..(first value removed) until $a is empty.

---

These two are still and will probably remain at 100 bytes:

for($a=[$n=$argv[1]];$n--;)for($i=count($a);$i--;)array_splice($a,$i,1,range(1,$a[$i]));print_r($a);

In each iteration loop backwards through array replacing each number with a range.

for($a=[$n=$argv[1]];$n--;)for($i=$c=0;$c=$a[$i+=$c];)array_splice($a,$i,1,range(1,$c));print_r($a);

In each iteration loop through array increasing index by previous number and replacing each indexed element with a range

Answer 26

Perl 5, 53 bytes

A subroutine:

{($i)=@_;for(1..$i){my@c;push@c,1..$_ for@_;@_=@c}@_}

See it in action as

perl -e'print "$_ " for sub{($i)=@_;for(1..$i){my@c;push@c,1..$_ for@_;@_=@c}@_}->(3)'

Answer 27

Ruby, 61 bytes

def f(n);a=[n];n.times{a=a.map{|i|(1..i).to_a}.flatten};a;end