圖解Java中歸並排序算法的原理與實現

package com.algorithm.tenSortingAlgorithm;

import java.util.Arrays;

public class MergeSort {
    private static void mergeSort(int[] arr, int low, int high) {
        if (low < high) { //當子序列中隻有一個元素時結束遞歸
            int mid = (low + high) / 2; //劃分子序列
            mergeSort(arr, low, mid); //對左側子序列進行遞歸排序
            mergeSort(arr, mid + 1, high); //對右側子序列進行遞歸排序
            merge(arr, low, mid, high); //合並
        }
    }

    private static void merge(int[] arr, int low, int mid, int high) {
        int[] temp = new int[arr.length]; //輔助數組
        int k = 0, i = low, j = mid + 1; //i左邊序列和j右邊序列起始索引,k是存放指針
        while (i <= mid && j <= high) {
            if (arr[i] <= arr[j]) {
                temp[k++] = arr[i++];
            } else {
                temp[k++] = arr[j++];
            }
        }
        //如果第一個序列未檢測完，直接將後面所有元素加到合並的序列中
        while (i <= mid) {
            temp[k++] = arr[i++];
        }
        //同上
        while (j <= high) {
            temp[k++] = arr[j++];
        }
        //復制回原數組
        for (int t = 0; t < k; t++) {
            arr[low + t] = temp[t];
        }
    }

    public static void main(String[] args) {
        int[] arr = {1,28,3,21,11,7,6,18};
        mergeSort(arr, 0, arr.length - 1);
        System.out.println(Arrays.toString(arr));
    }
}