What are the techniques to master the quick sort algorithm in PHP and improve the speed of sorting array elements?

What are the techniques to master the quick sort algorithm in PHP and improve the speed of sorting array elements?

Quick sort is a commonly used and efficient sorting algorithm. Its basic idea is to separate the sequence to be sorted into two independent parts through one pass of sorting. All elements in one part are smaller than the elements in the other part. Then the two parts are sorted recursively to achieve the purpose of ordering the entire sequence. In PHP, we can improve the speed of sorting array elements by mastering the quick sort algorithm and some optimization techniques.

The implementation of the quick sort algorithm mainly includes the following steps:

1. Select a benchmark element, usually the first element of the sequence to be sorted.
2. Set two pointers, one pointing to the starting position of the sequence and one pointing to the end position of the sequence.
3. According to the value of the reference element, divide the entire sequence into two parts. Those smaller than the reference element are placed on the left side of the sequence, and those larger than the reference element are placed on the right side of the sequence.
4. Recursively sort the left and right parts until each subsequence has only one element.

The following is a specific PHP code example that implements the quick sort algorithm:

function quick_sort(&$arr, $left, $right) {
    if ($left < $right) {
        $pivot = partition($arr, $left, $right);
        quick_sort($arr, $left, $pivot - 1);
        quick_sort($arr, $pivot + 1, $right);
    }
}

function partition(&$arr, $left, $right) {
    $pivot = $arr[$left];  // 选择第一个元素作为基准元素
    while ($left < $right) {
        // 从右往左找到第一个小于基准元素的值
        while ($left < $right && $arr[$right] >= $pivot) {
            $right--;
        }
        // 将小于基准元素的值移到左边
        $arr[$left] = $arr[$right];
        // 从左往右找到第一个大于基准元素的值
        while ($left < $right && $arr[$left] <= $pivot) {
            $left++;
        }
        // 将大于基准元素的值移到右边
        $arr[$right] = $arr[$left];
    }
    // 将基准元素放到正确的位置上
    $arr[$left] = $pivot;
    // 返回基准元素的位置
    return $left;
}

// 使用示例
$arr = [6, 1, 9, 3, 2, 8, 7, 5, 4];
quick_sort($arr, 0, count($arr) - 1);
print_r($arr);  // 输出 [1, 2, 3, 4, 5, 6, 7, 8, 9]

The above code implements the quick sort algorithm and sorts a sample array. The time complexity of the quick sort algorithm is O(nlogn), which is a very efficient sorting algorithm.

In actual use, some optimizations can be made to the quick sort algorithm to improve the speed of sorting, for example:

1. Randomly select the base element: not only select the first element as Benchmark, you can randomly select an element as the benchmark to avoid worst-case time complexity degradation.
2. Use insertion sort for small-scale subsequences: When the size of the sequence to be sorted is small, the recursive call overhead of quick sort is large. It can be judged that when the size of the sequence is less than a certain threshold, use insertion sort instead of recursive calls. .
3. Optimize recursive calls: During recursive calls, you can sort longer subsequences first, and then sort shorter subsequences to reduce the height of the recursive tree and improve the sorting speed.

To sum up, mastering the quick sort algorithm and its related optimization techniques in PHP can improve the speed of sorting array elements. In practical applications, different optimization methods can be selected according to specific scenarios to achieve higher sorting efficiency.

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