Multiple sort implementations in one class

Sort.class.php

<?php
class Sort {

    public static function radix_sort($input) {
        $min = min($input);
        $max = max($input);
        $temp = array_fill($min, $max - $min + 1, 0);
        foreach ($input as $key => $val) {
            $temp[$val]++;
        }

        $input = array();
        foreach ($temp as $key => $val) {
            if ($val == 1) {
                $input[] = $key;
            } else {
                while ($val--) {
                    $input[] = $key;
                }
            }
        }
        return $input;
    }

    public static function merge_sort($arr) {
        if (count($arr) <= 1) {
            return $arr;
        }
        $left = array_slice($arr, 0, (int) (count($arr) / 2));
        $right = array_slice($arr, (int) (count($arr) / 2));
        $left = self::merge_sort($left);
        $right = self::merge_sort($right);
        $output = self::merge($left, $right);
        return $output;
    }

    private static function merge($left, $right) {
        $result = array();
        while (count($left) > 0 && count($right) > 0) {
            if ($left[0] <= $right[0]) {
                array_push($result, array_shift($left));
            } else {
                array_push($result, array_shift($right));
            }
        }
        array_splice($result, count($result), 0, $left);
        array_splice($result, count($result), 0, $right);
        return $result;
    }

}