<?php
function is_anagram($string1,$string2){
  $lenString1 = strlen($string1);
  $lenString2 = strlen($string2);
  if($lenString1 == 0 || $lenString2 == 0 || $lenString1 != $lenString2 ){
    return false;
  }
  $acumulator = [];
  for( $i = 0; $i <= $lenString1; $i++ ) {
    $char = substr( $string1, $i, 1 );
    $char2 = substr( $string2, $i, 1 );
    $acumulator[$char] = !isset($acumulator[$char]) ? 1 : ++$acumulator[$char];
    $acumulator[$char2] = !isset($acumulator[$char2]) ? -1 : --$acumulator[$char2];
    if(isset($acumulator[$char]) && $acumulator[$char] == 0) unset($acumulator[$char]);
    if(isset($acumulator[$char2]) && $acumulator[$char2] == 0) unset($acumulator[$char2]);

  }
  return empty($acumulator);
}