phpでマージソート

２つのテキストファイルをマージソート

<?

function mergeSort($list1, $list2){
    $mergedList = [];
    $n1 = 0;
    $n2 = 0;

    while($n1 < count($list1) && $n2 < count($list2)){
        if(strcmp($list1[$n1], $list2[$n2]) <= 0){
            $mergedList[] = $list1[$n1++];
        }else{
            $mergedList[] = $list2[$n2++];
        }
    }

    if($n1 < count($list1)){
        $mergedList = array_merge($mergedList, array_slice($list1, $n1));
    }
    if($n2 < count($list2)){
        $mergedList = array_merge($mergedList, array_slice($list2, $n2));
    }

    return $mergedList;
}

$list1 = file('hoge1.txt', FILE_IGNORE_NEW_LINES);
$list2 = file('hoge2.txt', FILE_IGNORE_NEW_LINES);

$mergedList = mergeSort($list1, $list2);

foreach($mergedList as $s) echo $s."\n";