Common Sorting Algorithms in PHP: Bubble Sort, Selection Sort, Insertion Sort, and Quick Sort

Bubble sort is a simple sorting algorithm that repeatedly steps through the list, compares adjacent elements and swaps them if they are in the wrong order.

function bubbleSort($arr) {
    $len = count($arr);
    for ($i = 1; $i < $len; $i++) {
        for ($k = 0; $k < $len - $i; $k++) {
            if ($arr[$k] > $arr[$k + 1]) {
                $tmp = $arr[$k + 1];
                $arr[$k + 1] = $arr[$k];
                $arr[$k] = $tmp;
            }
        }
    }
    return $arr;
}
$arr = array(1, 43, 54, 62, 21, 66, 32, 78, 36, 76, 39);
print_r($arr);

Selection sort works by repeatedly finding the minimum element from the unsorted portion and moving it to the beginning of the list.

function select_sort($arr) {
    for ($i = 0, $len = count($arr); $i < $len - 1; $i++) {
        $p = $i;
        for ($j = $i + 1; $j < $len; $j++) {
            if ($arr[$p] > $arr[$j]) {
                $p = $j;
            }
        }
        if ($p != $i) {
            $tmp = $arr[$p];
            $arr[$p] = $arr[$i];
            $arr[$i] = $tmp;
        }
    }
    return $arr;
}
$arr = array(1, 43, 54, 62, 21, 66, 32, 78, 36, 76, 39);
print_r($arr);

Insertion sort builds a sorted sequence one element at a time by taking each unsorted element and inserting it into its correct position within the already sorted part.

function insert_sort($arr) {
    $len = count($arr);
    for ($i = 1; $i < $len; $i++) {
        $tmp = $arr[$i];
        for ($j = $i - 1; $j >= 0; $j--) {
            if ($tmp < $arr[$j]) {
                $arr[$j + 1] = $arr[$j];
                $arr[$j] = $tmp;
            } else {
                break;
            }
        }
    }
    return $arr;
}
$arr = array(1, 43, 54, 62, 21, 66, 32, 78, 36, 76, 39);
print_r($arr);

Quick sort is a divide‑and‑conquer algorithm that selects a pivot element, partitions the remaining elements into those less than and greater than the pivot, and then recursively sorts the sub‑arrays, achieving average‑case O(n log n) performance.

function quick_sort($arr) {
    if (!is_array($arr)) {
        return false;
    }
    $length = count($arr);
    if ($length <= 1) {
        return $arr;
    }
    $left = $right = array();
    for ($i = 1; $i < $length; $i++) {
        if ($arr[$i] < $arr[0]) {
            $left[] = $arr[$i];
        } else {
            $right[] = $arr[$i];
        }
    }
    $left = quick_sort($left);
    $right = quick_sort($right);
    return array_merge($left, array($arr[0]), $right);
}
$arr = array(1, 43, 54, 62, 21, 66, 32, 78, 36, 76, 39);
print_r($arr);