Reverse a 1-dimensional array

Question

Note: This challenge is not the same.

Challenge

Believe it or not, we haven't got ONE challenge for reversing one-dimensional arrays (although we've got one for n-dimensional ones)! This should operate only on the 1st dimension, not on all dimensions of an array.

Rules

• Standard loopholes are denied
• [[1, 2], [3, 4]] becomes [[3, 4], [1, 2]], not [[4, 3], [2, 1]].
• This is code-golf, but no answer is accepted. Go beat the others!
• You can get the array any way, except hardcoding. You can also get a string and process it.
• The input will be an array (yes, commas or no commas, it needs to be an array).

Test cases

These are the test cases:

[1, 2, 3, 4]
[1, 2, 'hello', 'world!']
[[1, 2, 3, 4], [2, 3, 4, 1]]
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23]

These are the supposed results:

[4, 3, 2, 1]
['world!', 'hello', 2, 1]
[[2, 3, 4, 1], [1, 2, 3, 4]]
[23, 22, 21, 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1]

You may accept input as [1 2 3 4], or even 1 2 3 4, or any other form or array your language has.

Answer 1

Jelly, 1 byte

Ṛ

Try it online! It reverses an array. _{(yay this is my first Jelly answer!)}

Answer 2

Pyth, 2 1 bytes

1 byte off thanks to Doorknob

_

_ is reverse, and Pyth takes implicit input. Yes, my first Pyth answer is an underscore.

Answer 3

Python 2, 8 bytes

reversed

This is too short.

Answer 4

𝔼𝕊𝕄𝕚𝕟, 3 bytes

ᴚ

Literally reverses array. Implicitly performs I/O.

Answer 5

Python 3, 16 bytes

lambda x:x[::-1]

This isn't even enough characters to post as an answer.

Answer 6

C, 65 bytes

Takes a pointer to the start of the list and a list length.

void f(int*a,int s){int t=*a;*a=a[--s];a[s--]=t;if(s>1)f(a+1,s);}

This is a recursive algorithm that swaps the first element with the last, and then runs the same function on the middle.

Ungolfed:

void f(int* a, int s){
  int t = a[0];
  a[0] = a[--s];
  a[s--] = t;
  if(s > 1){
    f(a + 1, s - 2);
  }
}

Answer 7

Python 2, 19 bytes

print input()[::-1]

Answer 8

05AB1E, 1 byte

Code:

R

Try it online!.

Answer 9

Brachylog, 2 bytes

r.

which expects a list as Input and unifies the reverse with the Output.

Alternative

rw

which expects a list as Input and writes the reverse to STDOUT.

Answer 10

Java 8, 62 38 30 bytes

java.util.Collections::reverse

Modifies the input-ArrayList instead of returning a new one to save bytes.

-8 bytes thanks to @OliverGrégoire.

Try it here.

---

With an array as input instead of ArrayList (62 bytes):

import java.util.*;a->{Collections.reverse(Arrays.asList(a));}

Modifies the input-array instead of returning a new one to save bytes.

Try it here.

---

Looping over the array to reverse it would be 75 69 bytes instead:

a->{Object t;for(int i=0,j=a.length;i<--j;a[i++]=a[j],a[j]=t)t=a[i];}

Try it here.

-5 bytes thanks to @OliverGrégoire.

Answer 11

Ruby, 14 bytes

you can't get simpler than this:

->a{a.reverse}

Answer 12

JavaScript ES6, 14 bytes

x=>x.reverse()

Simple enough. Anonymous lambda that reverses an array.

Answer 13

Actually, 1 byte

R

Reverses the input list. These are words to make this answer long enough.

Answer 14

SmileBASIC, 34 bytes

DEF R A
DIM T[LEN(A)]RSORT T,A
END

RSORT actually just sorts the arrays, and then reverses them.

Cheating answer: (requires turning the screen upside down):

LINPUT S$ATTR 2?S$

Answer 15

Python 3, 12 bytes

list.reverse

Surprised nobody else used this. Reverses in place, but I don't think there are any restrictions on that.

Answer 16

Jolf, 1 + 1 = 2 bytes

_

Try it here! (bonus for polyglot with Pyth?) _ reverses (negates) an array. (Make sure pretty output is on.)

Answer 17

Pyke, 1 byte

_

Try it here!

Pyke has implicit input and output. Polyglot with Pyth, Jolf,

Answer 18

Perl 5, 11 bytes

A subroutine:

{reverse@_}

Answer 19

Keg, 1 byte

Nothing interesting. Keg has a built-in. (Since Keg does not have any other means of representing an array, let's assume the stack is the array (and in fact it is).)

?

Try it online!

Answer 20

Lua, 61 bytes

It beats C! \o/

It simply fill a new table in the reversed order.

function f(g)h={}for i=0,#g do h[#g-i]=g[i+1]end return h end

It could have been done by working on the pointer, suppressing the return statement and the new table definition, but it actually is longer by 2 bytes

function f(g)for i=1,#g/2 do x=#g-i+1g[x],g[i]=g[i],g[x]end end

Answer 21

MySQL, 64 bytes

set@=1;select a from(select a,@:=@+1 n from t order by n desc)u;

Tested on 5.6.24.

My first SQL answer; please provide feedback!

Answer 22

PHP, 17 bytes

$r=array_reverse;

call $r($array)

non-built-in version, 53 bytes:

function r($a){while($a)$b[]=array_pop($a);return$b;}

call r($array)

generator for PHP >= 5.5, 45 bytes

function y($a){while($a)yield array_pop($a);}

usage: foreach(y($array)as$v)var_dump($v);

Answer 23

Python, 16 bytes

lambda l:l[::-1]

Please examine this answer again. I was a bit lazy answering this :P

Thanks to 55749 (J843136028) for suggesting to convert this to a function :)

Answer 24

TI-Basic, 16 bytes

seq(Ans(I),I,dim(Ans),1,~1

No built-ins for reversing an array in TI-Basic...

Answer 25

Triangularity, 7 bytes

.).
IER

Try it online!

Answer 26

Dodos, 43 bytes

	main dab
	dab - a
-
	- dip
a
	dot dab
	dot

Try it online!

(the - function subtracts and a is lambda x: [sum(x[1:]), sum(x)]. So dab - a takes the first element of a list)

Answer 27

Preproc, 279 bytes

#define v(x)Z(Z(Z(Z(Z(x)))))
#define Z(x)Y(Y(Y(Y(Y(x)))))
#define Y(x)X(X(X(X(X(x)))))
#define X(x)e(e(e(e(e(x)))))
#define e(x,...)x
#define d()
#define s(x,y,...)y
#define r(x,y...)i(x,,R d d d d()()()()()(y)x)
#define C,
#define R()r
#define i(x,v...)s d()(C##x v)
v(r e()(I))

Try it online!

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Some notes.

• Because the language (one pass of the C preprocessor) is not Turing-complete (as far as I know), this can only process arrays up to a fixed size. That can be increased by making v(x) evaluate e(x) more times.
• Input on command line, separated with , (please only give non-negative integers)
• Output on stdout, separated with spaces.
• My first Preproc answer. Golfing suggestions are appreciated.
• I would appreciate it if someone explain why do I need 4 nested d.

Answer 28

MathGolf, 1 byte

Nothing interesting. MathGolf has a built-in.

x

Try it online!

Answer 29

APL (Dyalog Unicode), 1 byte

⊖

This works both on lists of lists and proper multi-dimensional arrays.

Try it online!

Answer 30

Molecule, 8 bytes

I"Ar"+`n

Explanation:

I"Ar"+`n
I"Ar"    Read input, append the command (reverse array) as a string.
     +   concatenate the 2 strings
      `n set the program's source code to that new string.

Simple I/O:

Input    | Output
[5 "n"]    [n 5.0]
['n 3]     [3.0 n]