Shortest way to reverse a number [closed]

Question

Write a function (or equivalent subprogram) to accept a single integer valued argument and return a (similarly typed) value found by reversing the order of the base-10 digits of the argument.

For example given 76543 return 34567

Answer 1

HTML 21 7 chars (1 char if I'm cheeky...)

‮n

replace n with your number

Answer 2

Python

int(str(76543)[::-1])

EDIT:

Shorter solution as suggested by @gnibbler:

int(`76543`[::-1])

or, if above is unclear:

x=76543
int(`x`[::-1])

Answer 3

Universal (language agnostic/independent)

If you want to use only numbers (avoid converting the number to string) and don't want to use some specific library (to be universal for any language):

x = 76543 # or whatever is your number
y = 0
while x > 0:
    y *= 10
    y += ( x %10 )
    x /= 10 # int division 

_{This is python, but it could be done in any language, because it's just a math method.}

Answer 4

Perl 6

+$n.flip

or:

$n.flip

for dynamically typed code.

Numbers got string methods due to language design.

Answer 5

J - 6 characters + variable

".|.":y

Where y is your value.

Answer 6

APL (3)

⍎⌽⍕

Usage:

⍎⌽⍕12345 => 54321

Answer 7

Vim

17 chars

:se ri<CR>C<C-R>"

Answer 8

PHP, 9 chars

(int)strrev(123);

To do it short where N is a constant:

strrev(N)

Answer 9

Befunge (3 characters)

Complete runnable program:

N.@

Where N is your number. Rules say "accept a single integer valued argument"; In Befunge you can only enter integers from 0 to 9.

Answer 10

Language-independent/mathematics

Inspired by Kiril Kirov's answer above. I got curious about the mathematical properties of reversing a number, so I decided to investigate a bit.

Turns out if you plot the difference n - rev(n) for natural numbers n in some base r, you get patterns like this ((n - rev(n)) / (r - 1), for r=10, wrapped at r columns, red denotes negative number):

This sequence could be generated as such (pseudocode):

for i=1 to r:
  output 0

for m=0, 1, …
  for k=1 to (r-1):
    for d=1 to r^m:
      for i=0 to (r-1):
        output (r-1) * (r+1)^m * (k - i)

If you store these values in a list/array, then n - arr[n] would get you the reversed form of n. Now, to "mathematically golf" this, we'd ideally want a closed-form expression that gives us the n:th value in the sequence, so that we could have a closed-form expression for solving the entire task. Unfortunately, I haven't been able to find such an expression... but it looks like it should be possible. :(

So yeah, not so much a code-golf as a mathematical curiosity, but if there is a closed-form expression of the above sequence it might actually be useful in proper PL golf submissions.

Answer 11

Haskell, 28 24 characters

f=read.reverse.show.(+0)

Answer 12

Scala - 33 Chars

def r(a:Int)=(a+"").reverse.toInt

Answer 13

Python 3+

Function form: 28 characters

r=lambda i:int(str(i)[::-1])

(Sub)program form: 25 characters

print(input()[::-1])

I consider some of the other Python examples to be cheating, or at least cheap, due to using hardcoded input and/or not fully satisfying the requirements.

Answer 14

Ruby (14)

x = 13456
x.to_s.reverse

Answer 15

It is possible to convert a number a string, then reverse the string and then convert that string back to number. This kind of feature is probably available in all language. If you are looking for a more mathematical method then this might help:

int n = 76543;
int r = 0;

while (n > 0) {
    r *= 10;
    r += n % 10;
    n /= 10;
}

Answer 16

Golfscript, 5 chars

`-1%~

This takes an argument on the stack and leaves the result on the stack. I'm exploiting the "subprogram" option in the spec: if you insist on a function, that's four chars more leaving it on the stack:

{`-1%~}:r

Answer 17

In shell scripting :

  echo "your number"|rev

Hope this was useful :)

Answer 18

Kinda late but

APL, 3

⍎⌽⍞

If you insists on a function

⍎∘⌽∘⍕

Answer 19

Mathematica, 14 bytes

IntegerReverse

This is not competing, because this function was only added in last week's 10.3 release, but for completeness I thought I'd add the only ever (I think?) built-in for this task.

Answer 20

mIRC 4.45 (35 Bytes)

$regsubex(12,/(.)/g,$mid(\A,-\n,1))

Answer 21

You could do the following in Java. Note that this converts to String and back and is not a mathematical solution.

public class test {
    public static int reverseInt(int i) {
        return Integer.valueOf((new StringBuffer(String.valueOf(i))).reverse().toString());
    }

    public static void main(String[] args) {
        int i = 1234;
        System.out.println("reverse("+i+") -> " + reverseInt(i));
    }
}

Answer 22

Depends on what you mean by short (javascript):

alert(String(123).split('').reverse().join('')),

Answer 23

Lua

Numbers and strings are interchangeable, so this is trivial

string.reverse(12345)

Answer 24

This one ACTUALLY takes an input, unlike some of the rest:

print`input()`[::-1]

Python btw.

Answer 25

Actionscript

43 characters. num as the parameter to the function:

num.toString().split('').reverse().join('')

Answer 26

Groovy

r={"$it".reverse() as BigDecimal}

assert r(1234) == 4321
assert r(345678987654567898765) == 567898765456789876543
assert r(345346457.24654654) == 45645642.754643543

Answer 27

Perl, 11 chars

The p flag is needed for this to work, included in the count.

Usage:

$ echo 76543 | perl -pE '$_=reverse'

Answer 28

Clojure (42 chars)

#(->> % str reverse(apply str)read-string)

Example usage:

(#(->> % str reverse(apply str)read-string) 98321)

returns 12389

Answer 29

Common Lisp - 60 chars

(first(list(parse-integer(reverse(write-to-string '4279)))))

will get you 9724.

Answer 30

BaCon

PRINT REVERSE$(STR$(76543))

Replace 76543 with any number.