Detailed explanation of merge sort algorithm in PHP

Detailed explanation of the merge sort algorithm in PHP

Introduction:
Sorting is one of the common basic problems in computer science. The orderly arrangement of data can improve the efficiency of retrieval, search and modification operations. . Among sorting algorithms, merge sort is a highly efficient and stable algorithm. This article will introduce the merge sort algorithm in PHP in detail, with code examples.

1. The principle of merge sort
   Merge sort is a divide-and-conquer algorithm. It divides the array to be sorted into two sub-arrays, merges and sorts the two sub-arrays respectively, and then merges the sorted The subarrays of are combined into a complete sorted array. The specific steps are as follows:
   1) Split: Divide the array into two sub-arrays until the length of the sub-array is 1.
   2) Merge: Merge two subarrays into an ordered array in order of size.
   3) Repeat the above steps until you get a complete ordered array.
2. Implementation of merge sort
   The following is the code implementation of merge sort in PHP:

function mergeSort($arr) {
    $length = count($arr);
    if ($length <= 1) {
        return $arr;
    }
    $mid = floor($length / 2);
    $left = array_slice($arr, 0, $mid);
    $right = array_slice($arr, $mid);
    $left = mergeSort($left); // 递归排序左半部分
    $right = mergeSort($right); // 递归排序右半部分
    return merge($left, $right); // 合并两个已排序的子数组
}

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

3. The time complexity of merge sort
   The time complexity of merge sort The degree is O(nlogn), where n is the length of the array to be sorted. The performance of merge sort is relatively stable and is not affected by the order of input data.
4. Application scenarios of merge sort
   The merge sort algorithm is suitable for scenarios that require a stable sorting algorithm and do not require high space complexity. For example, when sorting large-scale data, merge sort has better performance than other sorting algorithms.

Conclusion:
Merge sort is an efficient and stable sorting algorithm, and its specific implementation in PHP is relatively simple. Through the introduction of this article, I hope to have a deeper understanding of the merge sort algorithm and to be able to flexibly use this algorithm in actual development.

References:
[1] https://en.wikipedia.org/wiki/Merge_sort
[2] https://www.geeksforgeeks.org/merge-sort/

The above is the detailed content of Detailed explanation of merge sort algorithm in PHP. For more information, please follow other related articles on the PHP Chinese website!