(PHP) Merge Sort

merge_sort.php

<?php

function mergeSort(array &$array, int $front, int $end) {
    if ($front < $end) {
        $mid = (int) (($front + $end) / 2);
        mergeSort($array, $front, $mid);
        mergeSort($array, $mid + 1, $end);
        merge($array, $front, $mid, $end);
    }
}

function merge(array &$array, int $front, int $mid, int $end) {

    $array1 = array_slice($array, $front, $mid + 1);
    $array2 = array_slice($array, $mid + 1);

    $array1[] = PHP_INT_MAX;
    $array2[] = PHP_INT_MAX;

    $indexLeft = 0;
    $indexRight = 0;

    for ($i = $front; $i <= $end; $i++) {
        if ($array1[$indexLeft] < $array2[$indexRight]) {
            $array[$i] = $array1[$indexLeft];
            $indexLeft++;
        } else {
            $array[$i] = $array2[$indexRight];
            $indexRight++;
        }
    }
}


/** Main **/

$array = [10, 4, 11, 2, 1];

$front = 0;
$end = count($array) - 1;

mergeSort($array, $front, $end);
var_dump($array);
/*
array(5) {
  [0]=>
  int(1)
  [1]=>
  int(2)
  [2]=>
  int(4)
  [3]=>
  int(10)
  [4]=>
  int(11)
}
 */

refer to https://alrightchiu.github.io/SecondRound/comparison-sort-merge-sorthe-bing-pai-xu-fa.html