Home on the Range of Lists

Question

This challenge is simply to return a list of lists of integers, similar to the Python range function, except that each successive number must be that deep in lists.

Rules:

• Create a program or a non-anonymous function
• It should return or print the result
• The result should be returned in a list (of lists) or array (of arrays)
• If the parameter is zero, return an empty list
• This should be able to handle an integer parameter 0 <= n < 70.
  • (recursive solutions blow up pretty fast)
• The function should be callable with only the one parameter.
• Other behavior is undefined.
• This is code golf, so shortest code wins.

Example Call:

rangeList(6)
> [0, [1, [2, [3, [4, [5]]]]]]

Test Cases:

0  => []
1  => [0]
2  => [0, [1]]
6  => [0, [1, [2, [3, [4, [5]]]]]]
26 => [0, [1, [2, [3, [4, [5, [6, [7, [8, [9, [10, [11, [12, [13, [14, [15, [16, [17, [18, [19, [20, [21, [22, [23, [24, [25]]]]]]]]]]]]]]]]]]]]]]]]]]
69 => [0, [1, [2, [3, [4, [5, [6, [7, [8, [9, [10, [11, [12, [13, [14, [15, [16, [17, [18, [19, [20, [21, [22, [23, [24, [25, [26, [27, [28, [29, [30, [31, [32, [33, [34, [35, [36, [37, [38, [39, [40, [41, [42, [43, [44, [45, [46, [47, [48, [49, [50, [51, [52, [53, [54, [55, [56, [57, [58, [59, [60, [61, [62, [63, [64, [65, [66, [67, [68]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]

EDIT: isaacg's answer is the shortest so far. I'll update the accepted answer if anyone finds a shorter one in a language that existed at the posting of the challenge. Thanks for playing!

Answer 1

Pyth, 13 bytes

?hu]+HG_UQYQY

Try it here.

                 Implicit:
                 Q = eval(input())
                 Y = []
?           QY   If Q = 0, print Y
 h               else, print the first element of
  u     _UQY     the reduce, where Y is the initial value, over the list
                 reversed(range(Q))
   ]+HG          The reduce function: The list containing H prepended onto G.
                 The new number is inserted into the accumulated list,
                 then the resultant list is wrapped in another list.

Answer 2

APL (13 18)

Assuming ⎕IO=0:

f←{×⍵:⊃,∘⊂∘,/⍳⍵⋄⍬}

Explanation:

• ×⍵: if ⍵ is positive,
  • ,∘⊂∘,: join the left operand to the enclose of the right operand (i.e. x ,∘⊂∘, y = [x, [y]])
  • /: reduce
  • ⍳⍵: the numbers 0..⍵-1
  • ⊃: disclose the result
• ⋄: otherwise
  • ⍬: return the empty list
  • (this is necessary because / fails on ⍬, and ⍳0 gives the empty list.)

Addendum:

This function returns a nested array. However, it is a bit hard to tell this from APL's default output. It separates array items by spaces, so you can only tell nesting by double spaces. Here is a function that will take a nested array, and return a string, formatting the nested array in Python style (i.e. [a,[b,[c,...]]]).

arrfmt←{0=≡⍵:⍕⍵ ⋄ '[',(1↓∊',',¨∇¨⍵),']'}

Answer 3

Haskell, 67 bytes

data L=E|I Int|L[L] 
1#m=L[I$m-1]
n#m=L[I$m-n,(n-1)#m]
p 0=E
p n=n#n

In Haskell all elements of a list have to be of the same type, so I cannot mix integers with list of integers and I have to define a custom list type L. The helper function # recursively constructs the required list. The main function p checks for the empty list and calls # otherwise.

As new data types cannot be printed by default (the rules allow just to return the list), I add some more code for demonstration purpose:

data L=E|I Int|L[L] deriving Show

Now:

-- mapM_ (print . p) [0..5]
E
L [I 0]
L [I 0,L [I 1]]
L [I 0,L [I 1,L [I 2]]]
L [I 0,L [I 1,L [I 2,L [I 3]]]]
L [I 0,L [I 1,L [I 2,L [I 3,L [I 4]]]]]

Answer 4

Python, 48 bytes

f=lambda n,i=0:i<n and[i]+[f(n,i+1)]*(i<n-1)or[]

Using list multiplication to handle the special case.

Answer 5

Mathematica, 33

f@0={};f@1={0};f@n_:={0,f[n-1]+1}

Answer 6

CJam, 16 bytes

Lri){[}%]~;']*~p

This is a full program. It takes input via STDIN and prints the final array on to STDOUT.

As with the other CJam entry, 0 input will print "" as that is the representation of an empty array in CJam.

How it works:

L                   "Put an empty array on stack. This will be used for the 0 input";
 ri)                "Read the input, convert it to integer and increment it";
    {[}%            "Map over the array [0 ... input number] starting another array";
                    "after each element";
        ]~;         "Now on stack, we have input number, an empty array and the final";
                    "opening bracket. Close that array, unwrap it and pop the empty array";
           ']*~     "Put a string containing input number of ] characters and eval it";
                    "This closes all the opened arrays in the map earlier";
               p    "Print the string representation of the array";
                    "If the input was 0, the map runs 1 time and the ; pops that 1 array";
                    "Thus leaving only the initial empty array on stack";

Try it online here

Answer 7

JavaScript (ES6) 40

Recursive solution, pretty robust, no blows. Update Fails near 6500 with 'too much recursion'

F=n=>n--?(R=m=>m<n?[m,R(++m)]:[m])(0):[]

Iterative solution (45) No limits except memory usage

F=n=>{for(s=n?[--n]:[];n;)s=[--n,s];return s}

Try F(1000): FireBug console will not show you more than 190 nested arrays, but they are there

Answer 8

Java, 88 107 105 104 102 bytes

import java.util.*;int o;List f(final int n){return new Stack(){{add(n<1?"":o++);if(o<n)add(f(n));}};}

Pretty long compared to the others, though you can't do much better with Java. A check to determine whether to continue recursion is all it takes.

Answer 9

Python 2, 56 bytes

I suspect this could be golfed more.

f=lambda n,i=0:[i,f(n,i+1)]if i<n-1 else[i]if n>0 else[]

Tests:

# for n in (0,1,2,6,26,69): print n, '=>', f(n)
0 => []
1 => [0]
2 => [0, [1]]
6 => [0, [1, [2, [3, [4, [5]]]]]]
26 => [0, [1, [2, [3, [4, [5, [6, [7, [8, [9, [10, [11, [12, [13, [14, [15, [16, [17, [18, [19, [20, [21, [22, [23, [24, [25]]]]]]]]]]]]]]]]]]]]]]]]]]
69 => [0, [1, [2, [3, [4, [5, [6, [7, [8, [9, [10, [11, [12, [13, [14, [15, [16, [17, [18, [19, [20, [21, [22, [23, [24, [25, [26, [27, [28, [29, [30, [31, [32, [33, [34, [35, [36, [37, [38, [39, [40, [41, [42, [43, [44, [45, [46, [47, [48, [49, [50, [51, [52, [53, [54, [55, [56, [57, [58, [59, [60, [61, [62, [63, [64, [65, [66, [67, [68]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]

Answer 10

CJam, 17 bytes

I know Optimizer has found 16, but here is the best I can do:

{:I{[}%;{]}I1e>*}

This is a block, the closest thing to a function in CJam, which takes an integer on the stack, and leaves the desired nested array.

Use this program to test it, which puts the input on the stack, then calls the function and inspects the stack. Note that for 0, the stack output will contain "" - this is CJam's native representation of an empty array.

Answer 11

Ruby 46

f=->n{r=a=[]
(0...n).map{|i|a<<a=[i]}
r[0]||r}

Test it online: http://ideone.com/uYRVTa

Answer 12

C# - 100

Simple recursion. Check the zero special case and tick up with one variable, down with the other

object[]A(int y,int x=0){return y==0?new object[0]:y==1?new object[]{x}:new object[]{x,A(--y,++x)};}

C++ 87

(Visual C++ 2012)

int*A(int y,int x=0){int*b=new int{x};return!y?new int:--y?(b[1]=(int)A(y,++x))?b:0:b;}

This one is great, by which I mean byzantine, but it's the same basic idea as the c# one.

It's a C style array implementation, so it doesn't give you an array, it gives a int pointer, in which I was be storing both ints and other pointers. Like this: [0,*] *->[1,#] #-> [2,&] &-> etc, where the symbols are pseudo code for the int value of a pointer and the --> is where it pointers to in memory.

What an excellent easy to use implementation of c style jagged arrays I've devised (cough), but I maintain it's plausible enough to be within the rules of the question.

There's quite a lot of abusing ternary operators here, and also quite a lot of abusing the implicit cast from int to bool.

Example: If we let int *bar = (int*)A(3);, we can see:

bar
0x003bded8 {0}
((int*)bar[1])[0]
1
((int*)(((int*)bar[1])[1]))[0]
2

Which is pointer talk for [0,[1,[2]]].

Okay, fine. It doesn't actually have to be the awful. Here's some test code for running this c++ code:

int* GetNext(int* p){
  return (int*)p[1];
}

int main()
{
    auto x = 10;
    auto bar = A(x);

    for (int i = 1; i < x; i++){
        bar = GetNext(bar);
        std::cout << bar[0] << std::endl;
    }

}

Answer 13

Pyth, 15 bytes

?u[HG)_UtQ]tQQY

Which is really saying, in Python:

Q = eval(input())
if Q:
    print reduce(lambda G,H:[H,G], reverse(range(Q-1)), [Q-1])
else:
    print []

Answer 14

Haskell, 65 59 45 41 bytes

These nested lists are the same data-structure as rooted Trees, except that they can also be empty. Hence, we can use a list of them - also called a Forest to represent them.

(0!)
data T=N[T]Int
m!n=[N((m+1)!n)m|m<n]

Try it online!

Explanation

First of all we need to implement the Tree data type:

data Tree = Node [Tree] Int

From there it's just recursion using two parameters m (counting up) and n to keep track when to terminate:

m ! n= [ Node ((m+1)!n) m| m<n ]

Alternative, 61 bytes

import Data.Tree
f n=unfoldForest(\b->(b,[b+1|b<n-1]))[0|n>0]

Try it online!

Explanation

The function unfoldForest takes a list of initial values and a function x -> (y,[x]). For each initial value x it unfolds a tree using the function, producing a tuple (y,xs) where y will become the root and the xs are used to repeat the procedure:

unfoldForest (\b -> (b, [b+1 | b < 2]) [0]
  ≡ Node 0 [unfoldForest (\b -> (b, [b+1 | b < 2) [1]]
  ≡ Node 0 [Node 1 [unfoldForest (\b -> (b, [b+1 | b < 2) []]]
  ≡ Node 0 [Node 1 []]

Answer 15

Perl - 44

sub t{$r=[($t)=@_];$r=[$t,$r]while--$t>0;$r}

Will add explanation upon request. You can try it here.

Answer 16

JavaScript, 93 bytes

This isn't ideal, but I might as well give it a try. I'll try and golf this further later on, though for now I see no obvious way to.

function f(n){s='[';i=0;while(i<n-1)s+=i+++',[';s+=i||'';do{s+=']'}while(i--);return eval(s)}

Answer 17

Python, 75 bytes

This is just for show. It's the program I wrote when creating/designing this challenge.

f=lambda x,y=[]:y if x<1 else f(x-1,[x-2]+[y or[x-1]])if x>1 else y or[x-1]

Answer 18

Python, 44

f=lambda n,i=0:i<n-1and[i,f(n,i+1)]or[i][:n]

Recursively creates the tree. The [:n] at the end is to special-case n==0 into giving the empty list.

Answer 19

Joe, 8 bytes

Note: This is a non-competing answer. The first version of Joe was released after this question.

F:/+,M]R

What do we have here? F: defines a function F that is a chain of /+,, M] and R. When you call Fn, first Rn gets evaluated, returning range from 0 to n, exclusive. M] wraps each element to a list. Then the list is applied to /+,. x +, y returns x + [y]. / is a right fold. Thus, /+,a b c d... returns [a, [b, [c, [d...]]].

Example invocations (code is indented by 3, output by 0):

   F:/+,M]R
   F10
[0, [1, [2, [3, [4, [5, [6, [7, [8, [9]]]]]]]]]]
   F2
[0, [1]]
   F1
[0]
   F0
[]
   F_5
[0, [-1, [-2, [-3, [-4]]]]]

Answer 20

Ruby - Recursive version - 52

r=->(n,v=nil){(n-=1;n<0 ?v:r[n,(v ?[n,v]:[n])])||[]}

Non-recursive version: 66 62 57

r=->i{(i-1).downto(0).inject(nil){|a,n|a ?[n,a]:[n]}||[]}

Sample output (same for both versions)

p r[0]  # => []
p r[1]  # => [0]
p r[2]  # => [0, [1]]
p r[6]  # => [0, [1, [2, [3, [4, [5]]]]]]
p r[26] # => [0, [1, [2, [3, [4, [5, [6, [7, [8, [9, [10, [11, [12, [13, [14, [15, [16, [17, [18, [19, [20, [21, [22, [23, [24, [25]]]]]]]]]]]]]]]]]]]]]]]]]]
p r[69] # => [0, [1, [2, [3, [4, [5, [6, [7, [8, [9, [10, [11, [12, [13, [14, [15, [16, [17, [18, [19, [20, [21, [22, [23, [24, [25, [26, [27, [28, [29, [30, [31, [32, [33, [34, [35, [36, [37, [38, [39, [40, [41, [42, [43, [44, [45, [46, [47, [48, [49, [50, [51, [52, [53, [54, [55, [56, [57, [58, [59, [60, [61, [62, [63, [64, [65, [66, [67, [68]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]

The non-recursive version can handle arbitrarily large input.

p r[1000] # => [0, [1, [2, [3, [4, [5, [6, [7, [8, [9, [10, [11, [12, [13, [14, [15, [16, [17, [18, [19, [20, [21, [22, [23, [24, [25, [26, [27, [28, [29, [30, [31, [32, [33, [34, [35, [36, [37, [38, [39, [40, [41, [42, [43, [44, [45, [46, [47, [48, [49, [50, [51, [52, [53, [54, [55, [56, [57, [58, [59, [60, [61, [62, [63, [64, [65, [66, [67, [68, [69, [70, [71, [72, [73, [74, [75, [76, [77, [78, [79, [80, [81, [82, [83, [84, [85, [86, [87, [88, [89, [90, [91, [92, [93, [94, [95, [96, [97, [98, [99, [100, [101, [102, [103, [104, [105, [106, [107, [108, [109, [110, [111, [112, [113, [114, [115, [116, [117, [118, [119, [120, [121, [122, [123, [124, [125, [126, [127, [128, [129, [130, [131, [132, [133, [134, [135, [136, [137, [138, [139, [140, [141, [142, [143, [144, [145, [146, [147, [148, [149, [150, [151, [152, [153, [154, [155, [156, [157, [158, [159, [160, [161, [162, [163, [164, [165, [166, [167, [168, [169, [170, [171, [172, [173, [174, [175, [176, [177, [178, [179, [180, [181, [182, [183, [184, [185, [186, [187, [188, [189, [190, [191, [192, [193, [194, [195, [196, [197, [198, [199, [200, [201, [202, [203, [204, [205, [206, [207, [208, [209, [210, [211, [212, [213, [214, [215, [216, [217, [218, [219, [220, [221, [222, [223, [224, [225, [226, [227, [228, [229, [230, [231, [232, [233, [234, [235, [236, [237, [238, [239, [240, [241, [242, [243, [244, [245, [246, [247, [248, [249, [250, [251, [252, [253, [254, [255, [256, [257, [258, [259, [260, [261, [262, [263, [264, [265, [266, [267, [268, [269, [270, [271, [272, [273, [274, [275, [276, [277, [278, [279, [280, [281, [282, [283, [284, [285, [286, [287, [288, [289, [290, [291, [292, [293, [294, [295, [296, [297, [298, [299, [300, [301, [302, [303, [304, [305, [306, [307, [308, [309, [310, [311, [312, [313, [314, [315, [316, [317, [318, [319, [320, [321, [322, [323, [324, [325, [326, [327, [328, [329, [330, [331, [332, [333, [334, [335, [336, [337, [338, [339, [340, [341, [342, [343, [344, [345, [346, [347, [348, [349, [350, [351, [352, [353, [354, [355, [356, [357, [358, [359, [360, [361, [362, [363, [364, [365, [366, [367, [368, [369, [370, [371, [372, [373, [374, [375, [376, [377, [378, [379, [380, [381, [382, [383, [384, [385, [386, [387, [388, [389, [390, [391, [392, [393, [394, [395, [396, [397, [398, [399, [400, [401, [402, [403, [404, [405, [406, [407, [408, [409, [410, [411, [412, [413, [414, [415, [416, [417, [418, [419, [420, [421, [422, [423, [424, [425, [426, [427, [428, [429, [430, [431, [432, [433, [434, [435, [436, [437, [438, [439, [440, [441, [442, [443, [444, [445, [446, [447, [448, [449, [450, [451, [452, [453, [454, [455, [456, [457, [458, [459, [460, [461, [462, [463, [464, [465, [466, [467, [468, [469, [470, [471, [472, [473, [474, [475, [476, [477, [478, [479, [480, [481, [482, [483, [484, [485, [486, [487, [488, [489, [490, [491, [492, [493, [494, [495, [496, [497, [498, [499, [500, [501, [502, [503, [504, [505, [506, [507, [508, [509, [510, [511, [512, [513, [514, [515, [516, [517, [518, [519, [520, [521, [522, [523, [524, [525, [526, [527, [528, [529, [530, [531, [532, [533, [534, [535, [536, [537, [538, [539, [540, [541, [542, [543, [544, [545, [546, [547, [548, [549, [550, [551, [552, [553, [554, [555, [556, [557, [558, [559, [560, [561, [562, [563, [564, [565, [566, [567, [568, [569, [570, [571, [572, [573, [574, [575, [576, [577, [578, [579, [580, [581, [582, [583, [584, [585, [586, [587, [588, [589, [590, [591, [592, [593, [594, [595, [596, [597, [598, [599, [600, [601, [602, [603, [604, [605, [606, [607, [608, [609, [610, [611, [612, [613, [614, [615, [616, [617, [618, [619, [620, [621, [622, [623, [624, [625, [626, [627, [628, [629, [630, [631, [632, [633, [634, [635, [636, [637, [638, [639, [640, [641, [642, [643, [644, [645, [646, [647, [648, [649, [650, [651, [652, [653, [654, [655, [656, [657, [658, [659, [660, [661, [662, [663, [664, [665, [666, [667, [668, [669, [670, [671, [672, [673, [674, [675, [676, [677, [678, [679, [680, [681, [682, [683, [684, [685, [686, [687, [688, [689, [690, [691, [692, [693, [694, [695, [696, [697, [698, [699, [700, [701, [702, [703, [704, [705, [706, [707, [708, [709, [710, [711, [712, [713, [714, [715, [716, [717, [718, [719, [720, [721, [722, [723, [724, [725, [726, [727, [728, [729, [730, [731, [732, [733, [734, [735, [736, [737, [738, [739, [740, [741, [742, [743, [744, [745, [746, [747, [748, [749, [750, [751, [752, [753, [754, [755, [756, [757, [758, [759, [760, [761, [762, [763, [764, [765, [766, [767, [768, [769, [770, [771, [772, [773, [774, [775, [776, [777, [778, [779, [780, [781, [782, [783, [784, [785, [786, [787, [788, [789, [790, [791, [792, [793, [794, [795, [796, [797, [798, [799, [800, [801, [802, [803, [804, [805, [806, [807, [808, [809, [810, [811, [812, [813, [814, [815, [816, [817, [818, [819, [820, [821, [822, [823, [824, [825, [826, [827, [828, [829, [830, [831, [832, [833, [834, [835, [836, [837, [838, [839, [840, [841, [842, [843, [844, [845, [846, [847, [848, [849, [850, [851, [852, [853, [854, [855, [856, [857, [858, [859, [860, [861, [862, [863, [864, [865, [866, [867, [868, [869, [870, [871, [872, [873, [874, [875, [876, [877, [878, [879, [880, [881, [882, [883, [884, [885, [886, [887, [888, [889, [890, [891, [892, [893, [894, [895, [896, [897, [898, [899, [900, [901, [902, [903, [904, [905, [906, [907, [908, [909, [910, [911, [912, [913, [914, [915, [916, [917, [918, [919, [920, [921, [922, [923, [924, [925, [926, [927, [928, [929, [930, [931, [932, [933, [934, [935, [936, [937, [938, [939, [940, [941, [942, [943, [944, [945, [946, [947, [948, [949, [950, [951, [952, [953, [954, [955, [956, [957, [958, [959, [960, [961, [962, [963, [964, [965, [966, [967, [968, [969, [970, [971, [972, [973, [974, [975, [976, [977, [978, [979, [980, [981, [982, [983, [984, [985, [986, [987, [988, [989, [990, [991, [992, [993, [994, [995, [996, [997, [998, [999]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]

Both versions also gracefully accept negative numbers

p r[-5] # => []

Answer 21

PHP 5.4 (67 bytes):

I know, I know.

It's far from being the shortest answer.

But it works!

Here it is:

function F($n){for($c=$n?[--$n]:[];~$n&&$n--;$c=[$n,$c]);return$c;}

You can test it right here: https://ideone.com/42L35E (ignore the error)

---

Javascript (57 bytes):

This is the same exact code except that Javascript is picky about the return and I've reduced the variable names:

function F(n){for(c=n?[--n]:[];~n&&n--;c=[n,c]);return c}

See? Same code!

---

ES6 (49 bytes):

Basically the same exact code, but reduced for ES6:

F=n=>{for(c=n?[--n]:[];~n&&n--;c=[n,c]);return c}

Answer 22

Javascript (114 bytes):

Everybody else was doing recursive, so I wanted to try an iterative solution. I have too many special cases, though.

I hold a master list, and then loop and append new lists with new numbers.

function q(n){a=[];if(n==1)a=[0];else if(n!=0){a=[0,b=[]];for(i=1;i<n;){c=[];b.push(c);b.push(i++);b=c}}return a}

Answer 23

Common Lisp (95 bytes):

(defun f(n &optional(i 0))(cond((< i(1- n))(cons i(list(f n(1+ i)))))((> n 0)(list i))(t nil)))

Answer 24

JavaScript, 35 37 bytes

Recursive solution

f=(n,x=[])=>n?f(--n,x[0]?[n,x]:[n]):x

Try it online!

Answer 25

05AB1E, 11 bytes

_i¯ëFNI<α)R

Try it online or verify all test cases.

11-bytes alternative:

_i¯ëݨRvy)R

Try it online or verify all test cases.

Explanation:

05AB1E has no loops that go downwards, so to loop in the range (input, 0] I either have to:

• Create that range first (ݨR; create range [0, input], remove last item, reverse), and then loop over it (vy);
• Or loop in the range [0, input) instead (F), and take the absolute difference between the loop-index and the input-1 (NI<α).

_i          # If the (implicit) input is 0:
  ¯         #  Push the global array (empty by default)
 ë          # Else:
  F         #  Loop `N` in the range [0, (implicit) input):
   N        #   Push index `N`
    I<      #   Push input-1
      α     #   Take the absolute difference between the two
       )    #   Wrap everything on the stack into a list
        R   #   Reverse the list
            # (output the result implicitly after the if/loop)