Given an int input n, print out n*reversed(n)

Question

Given an integer n, print out n * reversed(n)

reversed(n) is the number you get when you reverse the digits of n.

---

reverse(512) = 215

reverse(1) = 1

reverse(101) = 101

>>>>>>>>

---

func(5) = 5*5 = 25

func(12) = 12*21 = 252

func(11) = 11*11 = 121

func(659) = 659*956 = 630004

Shortest code wins!

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Answer 1

05AB1E, 2 bytes

R*

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In 05AB1E, integers and strings are treated as equivalent types, so reversal (R) converts to string and reverses, whilst multiplication (*) treats the reverse and the input as integers.

Answer 2

JavaScript (SpiderMonkey), 45 35 33 28 bytes

n=>n*[...n].reverse().join``

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• Saved 2 bytes thanks to dennis
• Saved 8 bytes thanks to kamoroso94
• Saved 2 bytes thanks to ATaco
• Saved 5 bytes thanks to Shaggy

Answer 3

Jelly, 3 bytes

×ṚḌ

I'm new to Jelly, so please let me know if there is a way to do this in 1 or 2 bytes!

Try it online!

Explanation

×ṚḌ    (Input: 12)

 Ṛ     Reversed decimal digits (Stack: [2, 1])
×      Multiply by input       (Stack: [24, 12])
  Ḍ    Convert to decimal      (Stack: 252)
       Implicit print

Answer 4

Ruby, 25 24 bytes

->n{n*eval(n.digits*'')}

Try It Online!.

Integer#digits returns a list of reversed digits, so further reversing is not necessary.

Thanks to @benj2240 for golfing a byte!

Answer 5

Perl 5, 11 + 1 (-p) = 12 bytes

$_*=reverse

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Answer 6

ARBLE, 12 bytes

Takes input as an int.

a*reverse(a)

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Answer 7

Python 3, 35 28 bytes

lambda m:m*int(str(m)[::-1])

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^{Saved 7 bytes by fixing a bug pointed out by Dennis.}

Answer 8

J, 7 bytes

*|.&.":

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Couldn't think of a shorter way, though I feel like this is pretty elegant.

Explanation

*|.&.":
   &.":  Convert to string, apply next function, then undo conversion
 |.      Reverse
*        Multiply by input

Answer 9

Haskell, 27 23 bytes

4 bytes saved thanks to Lynn and Laikoni

(*)=<<read.reverse.show

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Answer 10

Perl 6, 10 bytes

{$_*.flip}

Try it

Expanded

{       # bare block lambda with implicit parameter $_
  $_
  *
  .flip # implicit method call on $_
}

Answer 11

bash, 52 48 bytes

for((i=n=$1;r=r*10+i%10*n,i/=10;));{ :;};echo $r

Answer 12

C# .NET, 55 bytes

n=>{int i=n,j=0;for(;i>0;i/=10)j=j*10+i%10;return n*j;}

Explanation:

Try it here.

n=>{           // Method with integer as both parameter and return-type
  int i=n,     //  Integer `i` (starting at the input)
      j=0;     //  Integer `j` (starting at 0)
  for(;i>0;    //  Loop as long as `i` is not 0
      i/=10)   //    After every iteration: Remove the last digit of `i`
    j=j*10     //   Add a trailing zero to `j`,
      +i%10;   //   and then sum this new `j` with the last digit of `i`
               //  End of loop (implicit / single-line body)
  return n*j;  //  Return the input multiplied with `j`
}              // End of method

Answer 13

Ohm v2, 2 bytes

œΠ

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Explanation:

œΠ   Main wire, arguments: n

œ    Pushes [n, n.reverse]
 Π   Multiplies that array together
     Implicit output

Answer 14

Batch, 87 bytes

@set s=%1
@set r=
:l
@set/ar=r*10+s%%10,s/=10
@if %s% gtr 0 goto l
@cmd/cset/a%1*r

Need to take the arithmetic route here as string reversal fails for some numbers such as 80.

Answer 15

C (gcc), 49 bytes

i,a;f(n){for(i=0,a=n;a>0;a/=10)i=i*10+a%10;n*=i;}

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Answer 16

LISP, 91 64 bytes

(defun R (N)(defvar M (write-to-string N)) (parse-integer (reverse M))) (write (* x (R x)))

(defun R(N)(write(* N(parse-integer(reverse(write-to-string N))))))

Where x N is your integer you want to work with, of course.

I'm pretty new to programming, but I've found that trying these Code Golf problems has been nice practice. Is there something I'm missing that could help with this?

EDIT: Thanks to some tips from ceilingcat, I was able to shave off a few bytes. Old program preserved in strikethrough for reference.

Answer 17

Bash + GNU utilities, 18

bc<<<$1*`rev<<<$1`

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Answer 18

Batch, 150 125 121 bytes (+ 5 bytes? cmd/q)

set l=%1
set n=0
set r=
:L
call set t=%%l:~%n%,1%%%
set/an+=1
if [%t%] neq [] set r=%t%%r%&goto L
set/ar=%r%*%l%
echo %r%

Saved 25 bytes thanks to user202729!

Saved 4 bytes thanks to Matheus Avellar!

Answer 19

><>, 41 39 Bytes

:&>:a%:}-\
/~\?)0:,a/
>l1-?\&*n;
\ +*a/

How it works:

:&

Assume input has been pushed to the stack (https://codegolf.meta.stackexchange.com/a/8493/76025). Duplicate it and store a copy in the register.

   >:a%:}-\
   \?)0:,a/

Converts this to its individual digits, leaving them on the stack.

/~
>l1-?\
\ +*a/

The top value will always be a zero due to the number-to-digit conversion process; drop it from the stack. Now, while the length is >1, multiply the first item by ten and add it to the item below it. This results in the number reversed.

      &*n;

Multiply the original number by the reverse, print the answer, and stop.

Answer 20

Vyxal, 2 bytes

Ṙ*

Try it online, or verify all test cases.

Answer 21

Julia, 28 bytes

~n=parse(Int,reverse("$n"))n

Attempt This Online!

Answer 22

Leaf Lang, 41 bytes

Note: The interpreter does not have a stable release. If I introduce a breaking change I will update this post.

import"string.lf"argv:o o reverse o*print

Explained:

import "string.lf" - import stdlib's string.lf
argv               - push all of argv onto stack
:o                 - set o to top value from stack (pops top)
o                  - push o to top of stack
reverse            - reverse the string
o                  - push o to top of stack
*                  - leaf lang will implicitly convert strings to numbers when applicable
print              - print top value of stack with no newline

Ungolfed:

import "string.lf"
argv : num
num reverse num * 
print

Answer 23

Mathematica, 19 bytes

# IntegerReverse@#&

Takes an integer input.

Answer 24

cQuents 0, 8 bytes

#|1:A\rA

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Explanation

#|1:      Output first term in sequence
    A\rA  Each term in the sequence equals:
           A * \reverse(A)

Answer 25

Ly, 7 bytes

nsSrJl*

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Answer 26

Casio-Basic (fx-CP400), 44 bytes

ExpToStr n,a
StrInv a,a
Print n*strToExp(a)

There's no built-in for reversing an integer, but there is one for reversing a string.

ExpToStr n,a turns n into a string and stores it in a, then StrInv a,a overwrites a with the reversed version of itself. The last line turns a into a number, and prints n*a.

43 bytes for the code, +1 to input n into the parameters box.

Answer 27

Japt, 2 bytes

Takes input as a string, outputs an integer.

*w

Try it

Answer 28

MATLAB/Octave, 33 31 bytes

@(n)str2num(flip(int2str(n)))*n

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Octave/MATLAB anonymous function. This is a pretty naïve approach - converts the integer to a string, flips the string, converts the result back to an integer and multiplies it by the original.

---

• Save 2 bytes by using flip instead of fliplr.

Answer 29

Python 2, 25 bytes

lambda n:n*int(`n`[::-1])

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Answer 30

PHP, 23+1 bytes

<?=$argn*strrev($argn);

Save to file and run as pipe with -nF.