Project Euler.net Answers

Problem 4

Solved on 2/26/2008

A palindromic number reads the same both ways. The largest palindrome made from the product of two 2-digit numbers is 9009 = 91 × 99.

Find the largest palindrome made from the product of two 3-digit numbers.

$answer = 0;
for($oc = 999; $oc>1; $oc--){
  for($ic = 999; $ic>1; $ic--){
    if($this->isPal($ic*$oc)){
      if($ic*$oc > $answer){
        $answer = $ic*$oc;
        p1 = $ic;
        $p2 = $oc;
      }
    }
  }
}
function isPal($val){
  $rev = strrev($val);
  if(strlen($val) % 2 == 0){
    $length = strlen($val)/2;
    return (substr($val,0,$length) == substr($rev,0,$length));
  }else{
    $length = (strlen($val)-1)/2;
    return (substr($val,0,$length) == substr($rev,0,$length));
  }
}