Palindromic palindrome checker

Question

Write a program to test if a string is palindromic, with the added condition that the program be palindromic itself.

Answer 1

Ruby

z=gets;puts *z.reverse==z&&1||0||1&&z==esrever.z* stup;steg=z

Prints 1 if the input is a palindrome, 0 if it isn't. Input without linebreak.

Doesn't use any comments, instead it uses 2 tricks:

• Short-circuiting: 0 is true-ish in Ruby (only nil and false evaluate to false), so 1&&z==esrever.z* stup isn't evaluated and thus can't raise a runtime exception
• The splat/multiplication operator (*): To avoid a syntax error in z=esrever.z stup, we force the parser to parse this as z=esrever.z()*stup by adding a *. On the other side, the * is parsed as a splat operator, which in a function call splits an array in a series of parameters. If there's only one element instead of an array, it basically does nothing, so puts *foo is equivalent to puts foo.

Obvious solution using comments (prints true/false):

puts gets.reverse==$_#_$==esrever.steg stup

Answer 2

Perl

perl -nle "$s=$_ eq+reverse;print$s;s$tnirp;esrever+qe _$=s$"

no comment tricks, just cleverly abusing the substitution operator (hey, perl variables start with a $ too, so what?)

Answer 3

Python without comment

"a\";w=]1-::[w trinp;)(tupni_war=w;";w=raw_input();print w[::-1]==w;"\a"

I'm surprised that no one found that trick yet, it should work in most languages!

Answer 4

Python

s=raw_input();print'YNEOS'[s!=s[::-1]::2]#]2::]1-::[s=!s['SOENY'tnirp;)(tupni_war=s

Answer 5

Golfscript

.-1%=#=%1-.

• just with comment trick
• input without \n at the end
• perform matching char by char even for punctuations too
• returns 1 for success, 0 for fails

Answer 6

PHP

<?php eval/*/*/(';{$i=fgets(STDIN,2e9);};{$a="strrev";}{var_dump("{$i}"=="{$a($i)}");}/*}{*\{;("{(tupni$)a$}"=="{putni$}")ohce}{;"verrts"==a$};{;(9e2,NIDTS)stegf=i$);');/*\*\eval php?>

Uses some odd tricks to avoid the $ issue, technically isnt a palindrome as I had to sneak a ; in at the end.

 <?php $i = fgets(STDIN,2e9); echo $i == strrev($i);/*\;(i$)verrts == i$ ohce ;(9e2, NIDTS)stegf = $i php?>

This is a working one that uses PHP's /* */ comments and the fact that you don't need the end for them.

Answer 7

C

#include <stdio.h>                   //
#include <string.h>                  //
int main() {                         //
  char str[1024];                    //
  fgets(str, sizeof(str), stdin);    //
  int i = 0, j = strlen(str) - 2;    //
  for (; i < j; i++, j--)            //
    if (str[i] != str[j]) {          //
      printf("no\n");                //
      return 0;                      //
    }                                //
  printf("yes\n");                   //
}                                    //
//                                    }
//                   ;)"n\sey"(ftnirp  
//                                }    
//                      ;0 nruter      
//                ;)"n\on"(ftnirp      
//          { )]j[rts =! ]i[rts( fi    
//            )--j ,++i ;j < i ;( rof  
//    ;2 - )rts(nelrts = j ,0 = i tni  
//    ;)nidts ,)rts(foezis ,rts(stegf  
//                    ;]4201[rts rahc  
//                         { )(niam tni
//                  >h.gnirts< edulcni#
//                   >h.oidts< edulcni#

Running example:

$ gcc -std=c99 c.c && ./a.out 
blahalb
yes

Answer 8

PHP

echo strrev($z)==$z;#;z$==)z$(verrts ohce

Facts:

• $z string, the input string to check
• $t boolean, TRUE if the input string $z is palindrome, FALSE otherwise
• Using comments to help me make the code palindrome.
• Outputs $t
• Source itself is a palindrome

The reason why it will not be possible to implement palindromic palindrome checker in PHP it's because PHP variables are named starting with a $. You cannot end an identifier name with $ in PHP.

Answer 9

CoffeeScript

I actually struggled with the reverse spellings of 'split', 'reverse' and 'join' :\

p=(s)->s.split('').reverse().join('')==s#s==)''(nioj.)(esrever.)''(tilps.s>-)s(=p

Answer 10

Groovy

print args[0]==args[0].reverse()?1:0//0:1?)(esrever.]0[sgra==]0[sgra tnirp

Answer 11

JavaScript

alert('That is'+((X=prompt()).split('').reverse().join('')==X?'':"n't")+' a palindrome.')�)'.emordnilap a '+)"t'n":''?X==)''(nioj.)(esrever.)''(tilps.))(tpmorp=X((+'si tahT'(trela

The � in the middle is the null character.