Shortest way to reverse a number

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

Go back to the time the number was a string, then reverse the string — pmg, Commented Jun 11, 2011 at 10:54
The idea of a "shortest algorithm" is somewhat specious, especially if you'll allow "any language." Think up an algorithm, and I'll give you a DSL with an appropriate "~" operator ... — Pointy, Commented Jun 11, 2011 at 10:56
Just a notice: any number ending with 0 becomes a shorter number of digits when reversed... — powtac, Commented Jun 11, 2011 at 12:44
I know an algorithm that takes no time at all, but only works on palindromic numbers ;) — schnaader, Commented Jun 11, 2011 at 14:47
Found time to do the re-write myself. I hope this remain the puzzle that eltond meant to pose. — dmckee --- ex-moderator kitten, Commented Jun 12, 2011 at 0:37

Timtech · Accepted Answer · 2013-11-30 19:49:02Z

2

BaCon

PRINT REVERSE$(STR$(76543))

Replace 76543 with any number.

edited Nov 30, 2013 at 19:49

Timtech

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answered Jan 10, 2013 at 19:31

Pjot

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Community · Accepted Answer · 2020-06-17 09:04:33Z

2

Java

""+new StringBuilder(""+i).reverse();

edited Jun 17, 2020 at 9:04

CommunityBot

1

answered Aug 31, 2011 at 19:24

Ed Staub

1292 bronze badges

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rpax · Accepted Answer · 2014-07-02 13:03:48Z

2

Brainfuck, 11

>,[>,]<[.<]

answered Jul 2, 2014 at 13:03

rpax

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\$\begingroup\$ This accepts any string, not just numbers (ASCII 48-57). \$\endgroup\$
– Erik the Outgolfer
Commented Apr 16, 2016 at 8:00

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JohnE · Accepted Answer · 2015-06-22 18:15:03Z

2

K, 3 bytes:

.|$

Evaluate (.) the reverse (|) of casting to a string ($).

Usage example:

  .|$76543
34567

answered Jun 22, 2015 at 18:15

JohnE

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Community · Accepted Answer · 2020-06-17 09:04:33Z

2

rs, 20 bytes

#
+#(.*)(.)/\2#\1
#/

Technically, this doesn't count (rs was created earlier this year), but I didn't see any other regex-based answers, and I thought this was neat.

Live demo.

Explanation:

Insert a pound character at the beginning of the string. This is used as a marker.

+#(.*)(.)/\2#\1

Continuously prepend the last character of the main string to the area before the marker until there are no characters left.

#/

Remove the marker.

edited Jun 17, 2020 at 9:04

CommunityBot

1

answered Jun 23, 2015 at 2:02

kirbyfan64sos

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Community · Accepted Answer · 2017-04-13 12:39:04Z

2

TI-BASIC, 35 32 31 (or 28) bytes

Takes input from the calculator's answer variable, which is whatever was last evaluated (like _ in the interactive python shell).

fPart(.1int(Ans10^(seq(A,A,~int(log(Ans+.5)),not(Ans
sum(Ans10^(cumSum(1 or Ans

10^( is 2NDLOG and ~ is ( - ), next to ENTER. Everything else can be found in the 2ND0 catalog.

If the program doesn't have to handle the possibility of 0 as input, it can be reduced to 28 bytes by changing ~int(log(Ans+.5)),not(Ans to ~int(log(Ans)),0.
Credit goes partially to Thomas Kwa for helping to golf this.

edited Apr 13, 2017 at 12:39

CommunityBot

1

answered Jun 22, 2015 at 23:35

user39326

1

\$\begingroup\$ Doesn't work with 0; you could easily fix this by replacing log(Ans) with log(Ans+.5) and int( with iPart(. The shortest I found in a few minutes with a forwards list of digits was fPart(.1int(Ans10^(seq(A,A,~int(log(Ans)),0:sum(Ans10^(cumSum(1 or Ans; this can probably be improved. Overall, good work! \$\endgroup\$
– lirtosiast
Commented Jun 23, 2015 at 1:04
\$\begingroup\$ @ThomasKwa yep, using 0 for the end argument throws ERR:INCREMENT. You're right about not(Ans, though. \$\endgroup\$
– user39326
Commented Jun 23, 2015 at 4:55

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Community · Accepted Answer · 2020-06-17 09:04:33Z

2

ES6 Javascript, 31 bytes

x=>[...x+''].reverse().join('')

edited Jun 17, 2020 at 9:04

CommunityBot

1

answered Jul 4, 2015 at 14:31

Afonso Matos

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\$\begingroup\$ You could save 2 bytes by using .join`` instead of .join(''). Also, what do you mean with that comment: "This doesn't assume b is an integer." \$\endgroup\$
– Stefnotch
Commented Oct 22, 2015 at 17:20

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letsch323 · Accepted Answer · 2015-10-22 16:44:55Z

2

C++:

int reverse(int number, int number1, int number2){std::vector<int> v; v.push_back(number); v.push_back(number1); v.push_back(number2); std::cout << v[2] << v[1] << v[0]; return 0;}

answered Oct 22, 2015 at 16:44

letsch323

211 bronze badge

3

\$\begingroup\$ Welcome to Programming Puzzles and Code Golf letsch! It is customary to include the byte count along with your submission, as this question is a code-golf. You might want to format your header as such: # C++, <number of bytes> bytes \$\endgroup\$
– Conor O'Brien
Commented Oct 22, 2015 at 17:09
1

\$\begingroup\$ Adding to what Conor said, you should also attempt to make your code as short as possible since this is a code golf competition. You could start by removing unnecessary whitespace and using single letter names. \$\endgroup\$
– Alex A.
Commented Oct 22, 2015 at 18:58

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The Fifth Marshal · Accepted Answer · 2020-01-07 00:22:09Z

2

Pyth (3 chars)

Try it here

v_z

edited Jan 7, 2020 at 0:22

The Fifth Marshal

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answered Jun 22, 2015 at 17:48

cmxu

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Dan Diplo · Accepted Answer · 2011-06-11 14:41:47Z

1

C#

int reversed = Convert.ToInt32(String.Join<char>(null, 76543.ToString().Reverse()));

answered Jun 11, 2011 at 14:41

Dan Diplo

1113 bronze badges

\$\begingroup\$ int.Parse should be shorter. \$\endgroup\$
– Joey
Commented Jun 12, 2011 at 10:24
\$\begingroup\$ An anonymous user proposed editing this to int reversed = int.Parse(string.Join("", ("" + 76543).Reverse())); \$\endgroup\$
– Peter Taylor
Commented Sep 28, 2011 at 8:03

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frank · Accepted Answer · 2011-09-01 18:57:26Z

1

k4 - 6 characters

"I"$|$

Examples:

  "I"$|$76543
34567
  "I"$|$98765
56789

Explanation from right to left: ("I"$ = cast to integer)(| = reverse)($ = convert to string)

edited Sep 1, 2011 at 18:57

answered Aug 30, 2011 at 22:25

frank

212 bronze badges

\$\begingroup\$ It's possible to use . (eval) instead of "I"$, i.e. .|$. \$\endgroup\$
– coltim
Commented Oct 23, 2020 at 16:31

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Dynamic · Accepted Answer · 2011-11-23 15:44:32Z

1

Perl (19 chars)

Simple:

$x=reverse (98765);

edited Nov 23, 2011 at 15:44

answered Aug 19, 2011 at 19:08

Dynamic

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marinus · Accepted Answer · 2012-03-08 19:04:46Z

1

Bash (15)

read a;rev<<<$a

As a number of other entries do, '01234' becomes '43210' and '2340' becomes '0432'; i.e. in Python terms it does print reverse(raw_input()). If behaviour like print int(reverse(str(int(raw_input())))) is expected, it is a bit longer:

Takes care of trailing zeroes (36)

read a;sed s.^0*..\;s.0*$..<<<$a|rev

answered Mar 8, 2012 at 19:04

marinus

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\$\begingroup\$ I think right count is 3: rev alone will suffice \$\endgroup\$
– F. Hauri - Give Up GitHub
Commented Dec 1, 2013 at 13:24
\$\begingroup\$ “Write a function” – So I think the shortest solution is still 15 characters, but this way: r(){ rev<<<$1;}. (And even that is kind of cheating as the complete solutions is r(){ return `rev<<<$1`;}.) \$\endgroup\$
– manatwork
Commented Dec 2, 2013 at 9:40
1

\$\begingroup\$ @manatwork Shorter versions: r()(rev<<<$1) or r()(exit `rev<<<$1`). \$\endgroup\$
– jimmy23013
Commented Jul 1, 2014 at 21:20
\$\begingroup\$ Cool trick, @user23013. \$\endgroup\$
– manatwork
Commented Jul 2, 2014 at 10:57
\$\begingroup\$ str(int(raw_input())) really? [Python 2] [str(int(input()))] [from your example print int(reverse(str(int(raw_input()))))] \$\endgroup\$
– Erik the Outgolfer
Commented Apr 16, 2016 at 7:58

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tmartin · Accepted Answer · 2012-03-09 05:23:18Z

1

in Q (20 characters)

f:{"I"$reverse -3!x}

Sample Usage:

q)f 89478237
73287498

Use the k version of reverse (wrapped in parentheses) to make it shorter

{"I"$(|:) -3!x}

also just define it as a lambda to take 2 chars off for a total of 15

edited Mar 9, 2012 at 5:23

tmartin

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answered Mar 7, 2012 at 17:38

sinedcm

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jsvnm · Accepted Answer · 2012-03-12 09:12:43Z

1

ruby (26)

The existing ruby answer wasn't a function/lambda, so here goes:

f=->i{i.to_s.reverse.to_i}

answered Mar 12, 2012 at 9:12

jsvnm

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Thom Wiggers · Accepted Answer · 2013-12-01 01:54:54Z

1

Haskell, 61,23

Using the string reversing technique. digitToInt is available from the Data.Char library, and of course this code would be shorter if we'd be able to assume if Data.Char already was available.

-- original version 61 chars
foldl1((+).(*)10).map(Data.Char.digitToInt)$reverse$show 1234

--bonus foldonly version, 67 chars
foldl1((+).(*)10).foldl(flip((:).Data.Char.digitToInt))[]$show 1234

--FireFly's suggestion: 23 chars. Note that read's return type is `a`
-- so you might want to tack on a +1 on ghci etc so `Int` can be derived.
read.reverse.show$1234

edited Dec 1, 2013 at 1:54

answered Dec 1, 2013 at 0:49

Thom Wiggers

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1

\$\begingroup\$ Hm, why not read it back after reversing? I.e. read.reverse.show$1234. \$\endgroup\$
– FireFly
Commented Dec 1, 2013 at 1:19
\$\begingroup\$ hmm for some silly reason I thought read had to do with IO monads. You're right, read would work. \$\endgroup\$
– Thom Wiggers
Commented Dec 1, 2013 at 1:51
1

\$\begingroup\$ Added it. fold was more fun though :) \$\endgroup\$
– Thom Wiggers
Commented Dec 1, 2013 at 1:55

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Carlos Goce · Accepted Answer · 2013-12-02 09:11:37Z

1

Groovy 32

def r(n){print ((n+"").reverse())}

answered Dec 2, 2013 at 9:11

Carlos Goce

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blabb · Accepted Answer · 2015-06-23 06:51:39Z

1

POWERSHELL, 25

-join(Read-Host)[-1..-9]

a longer version to take arbitrary input , 36

-join($a=Read-Host)[-1..-$a.length]

usage

PS C:\> -join(Read-Host)[-1..-9]
123456789
987654321
PS C:\>

answered Jun 23, 2015 at 6:51

blabb

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Cooler Ranch · Accepted Answer · 2015-07-04 13:58:46Z

1

C# - 58

I think we need more C#

int.Parse(string.Concat(Enumerable.Reverse(x.ToString())))

edited Jul 4, 2015 at 13:58

answered Jul 4, 2015 at 4:44

Cooler Ranch

313 bronze badges

2

\$\begingroup\$ The spec requires a function or equivalent subprogram (a lambda would probably be acceptable, but a statement isn't); and it requires the return value to be similarly typed to the input (i.e. you're missing an int.Parse or a Convert.ToInt32). \$\endgroup\$
– Peter Taylor
Commented Jul 4, 2015 at 6:39
1

\$\begingroup\$ @CoolerRanch still a statement I think \$\endgroup\$
– Erik the Outgolfer
Commented Apr 16, 2016 at 8:06

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ErikDaParrot · Accepted Answer · 2024-11-23 19:22:58Z

1

Uiua, 4 bytes

⍜°⋕⇌

Try this online!

Explanation:

⍜°⋕⇌
⍜    => under (do 1st func, then the 2nd, then undo the 1st)
 °⋕  => number to string (1st func), undo func -> string back to number
   ⇌ => reverse (2nd func)

answered Nov 23 at 19:22

ErikDaParrot

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kba · Accepted Answer · 2011-11-29 05:53:34Z

0

Scheme, 75 characters

(string->number(list->string(reverse(string->list(number->string 76543)))))

edited Nov 29, 2011 at 5:53

answered Jun 12, 2011 at 16:59

kba

1013 bronze badges

\$\begingroup\$ You can probably remove all the spaces but the last one. \$\endgroup\$
– Omar
Commented Nov 29, 2011 at 5:50
\$\begingroup\$ Count in bytes, please. \$\endgroup\$
– Erik the Outgolfer
Commented Apr 16, 2016 at 8:03

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Community · Accepted Answer · 2017-04-13 12:39:14Z

0

k3, 4 chars

0$|$

0$|$76543 \-> gives 34567

See also the K4 solution here. The only difference (saving two chars) is that 0$ converts to int.

edited Apr 13, 2017 at 12:39

CommunityBot

1

answered Mar 11, 2012 at 21:54

Adam Schmideg

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l0n3sh4rk · Accepted Answer · 2012-05-02 14:39:24Z

0

PHP, 37

<?function f($n){return strrev($n);}

C, 44

x;m(n){for(;n;x=x*10+n%10,n/=10);return x;}

edited May 2, 2012 at 14:39

answered May 1, 2012 at 19:55

l0n3sh4rk

1,45711 silver badges13 bronze badges

\$\begingroup\$ Neither of these are functions, as specified. \$\endgroup\$
– Kevin Reid
Commented May 1, 2012 at 21:50
\$\begingroup\$ @KevinReid Rectified! \$\endgroup\$
– l0n3sh4rk
Commented May 2, 2012 at 14:47

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Ari B. Friedman · Accepted Answer · 2012-12-02 18:32:01Z

0

R (35 characters)

> cat(rev(strsplit("12345","")[[1]]))
5 4 3 2 1

With help from my friends in R chat.

edited Dec 2, 2012 at 18:32

answered Dec 2, 2012 at 13:22

Ari B. Friedman

1,1739 silver badges14 bronze badges

2

\$\begingroup\$ 12345->54321, not 12345->5 4 3 2 1. \$\endgroup\$
– Erik the Outgolfer
Commented Apr 16, 2016 at 8:04

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Timtech · Accepted Answer · 2013-11-30 16:11:55Z

0

Game Maker Language, 44

Replace 12345 with whatever number or variable you want:

n=12345while(n>0){r=r*10+(n mod 10)n div 10}

If you want to prompt for user input, use this 56 character long code instead:

n=get_string('','')while(n>0){r=r*10+(n mod 10)n div 10}

In both pieces of code, the reverse number is stored in r

answered Nov 30, 2013 at 16:11

Timtech

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\$\begingroup\$ The question specifically asks for "a function (or equivalent subprogram)" which takes "a single integer valued argument". Neither of your code snippets meet that spec. \$\endgroup\$
– Peter Taylor
Commented Nov 30, 2013 at 17:27
\$\begingroup\$ @PeterTaylor They're assumed to be scripts (function equivalents). \$\endgroup\$
– Timtech
Commented Nov 30, 2013 at 21:48

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Community · Accepted Answer · 2020-06-17 09:04:33Z

0

Rebol, 29

f: func[n][do reverse mold n]

Usage example in Rebol console:

>> f 76543
== 34567

If you only wanted this to work on integer input then....

f: func [n [integer!]] [do reverse mold n]

edited Jun 17, 2020 at 9:04

CommunityBot

1

answered Feb 27, 2014 at 22:27

draegtun

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M L · Accepted Answer · 2015-07-03 21:57:43Z

0

Julia, 23

r(x)=int(reverse("$x"))

$ interpolates an argument (or the result of a function) into a string, denoted by the double quotes. int() automatically deletes leading zeroes.

Example:

julia> x=1234567890;r(x)
987654321

or

julia> r(1234567890)
987654321

answered Jul 3, 2015 at 21:57

M L

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Community · Accepted Answer · 2020-06-17 09:04:33Z

0

TI-BASIC, 58 54

Input N:0:While N>0:Ans+E3fpart(N,10:N/10→N:End:Ans

Usage

prgmREVERSE
?598028
          820895
            Done

edited Jun 17, 2020 at 9:04

CommunityBot

1

answered Apr 8, 2014 at 15:51

Timtech

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mroman · Accepted Answer · 2015-10-22 17:03:17Z

0

Burlesque, 2 bytes

Certain built-ins treat numbers as list of digits. The reverse built-in for example treats integers as a list of digits and thus reverses integers.

blsq ) 76543<-
34567

(For characters <- switches case).

answered Oct 22, 2015 at 17:03

mroman

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Community · Accepted Answer · 2020-06-17 09:04:33Z

0

MATL, 3 bytes (non-competing)

VPU

This uses release 10.1.0 of the language/compiler, which is the current version at the time of writing.

Try it online!

Explanation

V   % implicitly input a number and convert to string
P   % flip
U   % convert to number and implicitly display

edited Jun 17, 2020 at 9:04

CommunityBot

1

answered Jan 24, 2016 at 5:14

Luis Mendo

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Stack Exchange Network

Shortest way to reverse a number

67 Answers 67

Java

Brainfuck, 11

K, 3 bytes:

rs, 20 bytes

Explanation:

TI-BASIC, 35 32 31 (or 28) bytes

ES6 Javascript, 31 bytes

Pyth (3 chars)

C#

Perl (19 chars)

Bash (15)

Takes care of trailing zeroes (36)

in Q (20 characters)

ruby (26)

Haskell, 61,23

C# - 58

Uiua, 4 bytes

k3, 4 chars

PHP, 37

C, 44

Game Maker Language, 44

Rebol, 29

Julia, 23

TI-BASIC, 58 54

Burlesque, 2 bytes

MATL, 3 bytes (non-competing)

Explanation

Your Answer

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Shortest way to reverse a number

67 Answers 67

Java

Brainfuck, 11

K, 3 bytes:

rs, 20 bytes

Explanation:

TI-BASIC, 35 32 31 (or 28) bytes

ES6 Javascript, 31 bytes

Pyth (3 chars)

C#

Perl (19 chars)

Bash (15)

Takes care of trailing zeroes (36)

in Q (20 characters)

ruby (26)

Haskell, 61,23

C# - 58

Uiua, 4 bytes

k3, 4 chars

PHP, 37

C, 44

Game Maker Language, 44

Rebol, 29

Julia, 23

TI-BASIC, 58 54

Burlesque, 2 bytes

MATL, 3 bytes (non-competing)

Explanation

Your Answer

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