QuickSort realized in PHP.

QuickSort.php

<?php
namespace Sort;

class QuickSorter {

    private $_array;

    public function __construct(array $array) {
        $this->_array = $array;
    }

    public function sort() {
        $this->quicksort(0, count($this->_array) - 1);
    }

    public function getArray() {
        return $this->_array;
    }

    public function printArray() {
        foreach($this->_array as $x) {
            echo "{$x} ";
        }
        echo "\n";
    }

    private function swap($index, $with) {
        $tmp = $this->_array[$index];
        $this->_array[$index] = $this->_array[$with];
        $this->_array[$with]  = $tmp;
    }

    private function split($left, $right, $pivotIndex) {
        $pivotValue = $this->_array[$pivotIndex];
        $storeIndex = $left;
        $this->swap($pivotIndex, $right);

        for($i = $left; $i < $right; $i++) {
            if($this->_array[$i] <= $pivotValue) {
                $this->swap($i, $storeIndex);
                $storeIndex++;
            }
        }

        $this->swap($storeIndex, $right);
        return $storeIndex;
    }

    private function quicksort($left, $right) {
        if($left < $right) {
            $pivotIndex = (int)($left + ($right - $left) / 2);
            $pivotNewIndex = $this->split($left, $right, $pivotIndex);
            $this->quicksort($left, $pivotNewIndex - 1);
            $this->quicksort($pivotNewIndex + 1, $right);
        }
    }
}

$sorter = new QuickSorter([-16, -9, 47, 25, -39, -43, 32, -23, -12, -50, -23, 0, 42, -40, 6, 49, 9, 10, -7, -20]);
$sorter->printArray();
$sorter->sort();
$sorter->printArray();