Check whether an integer is palindrome or not in PHP?

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How do I check if a number is a palindrome?

If an integer is to not allowed to be treated a string and typecasting is not allowed, how can we figure out whether the number is palindrome or not(in PHP)?

The program which I have come up with is:

function checkPalindrome($number){
    $reverse_number = 0;
    $number_backup  = $number;
    while($number > 0){
      $reverse_number = $reverse_number * 10 + $number % 10;
      $number /= 10;
    }
    return $reverse_number == $number_backup;
}

At step "$number/=10", the result generated won't be integer which is creating the problem.

Where do the not-string, no-typecasting constraints come from? Is this a [tag:homework] question? — David Thomas, May 21 '12 at 16:39
Is this a question for school? Why else would these restrictions apply? — DampeS8N, May 21 '12 at 16:41
In an interview? You are better off not getting the job... That's just a jerky thing to do to someone. (unless it is a code example you are meant to do and send back, in which case stop cheating.) — DampeS8N, May 21 '12 at 16:44
Its over and not getting job anyway:). Just curious to know the answer now. — sushil, May 21 '12 at 16:47
The algorithm is language-agnostic, so just add dollar signs or whatever's necessary to make it PHP. — Wiseguy, May 21 '12 at 16:57
@Wiseguy: Try it. It doesn't work. The difference is that in PHP, you have to do: `$num = ($num - $dig) / 10;`. — Travesty3, May 21 '12 at 16:59
Or `$num = floor($num/10);` would work as well. I don't think that would violate the rules of "no typecasting." — Travesty3, May 21 '12 at 17:08

Emil Vikström · Accepted Answer · 2012-06-21T12:10:13.570

6

If you are not allowed to typecast and string-handling is forbidden, you need to do some extra calculations:

while($number > 0){
  $lsd = $number % 10;
  $reverse_number = $reverse_number * 10 + $lsd;
  $number = ($number - $lsd) / 10;
}

edited Jun 21 '12 at 12:10

answered May 21 '12 at 16:46

Emil Vikström

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Great! This solves the problem. – sushil May 21 '12 at 16:51
Cole, *least significant digit* :-) – Emil Vikström May 21 '12 at 16:57

Check whether an integer is palindrome or not in PHP?

1 Answers1