diagonal array summation

diagonal_array_summation.php

<?php

$handle = fopen ("php://stdin","r");
fscanf($handle,"%d",$n);
$a = array();
for($a_i = 0; $a_i < $n; $a_i++) {
   $a_temp = fgets($handle);
   $a[] = explode(" ",$a_temp);
  array_walk($a[$a_i],'intval');
}

$left[0] = array_sum( 
            array_map(function($row, $index){
                        return $row[$index];
                      }, $a, array_keys($a)
                     ) 
         );

$right[1] = array_sum( array_map(function($row, $index){
  return $row[$index];
}, $a, array_reverse(array_keys($a))) );
    
    $result = array_diff($right, $left);
    print_r($result);
?>