算法之归并排序

package com.ebiz.sort;import java.util.Arrays;/*** @author YHj* @create 2019-09-03 22:21*  /*** 归并排序（递归）** ①. 将序列每相邻两个数字进行归并操作，形成 floor(n/2)个序列* ②. 执行①直到每组有一个元素
 * ③. 各组之间进行比较* ④. 重复步骤③，直到所有元素排序完毕。*/public class Merge {public static void main(String[] args) {int [] arr = {8,4,5,7,1,3,6,2,9};mergingSort(arr);}public static int[] mergingSort(int[] arr){if(arr.length <= 1){return arr;}int num = arr.length >> 1;int[] leftArr = Arrays.copyOfRange(arr, 0, num);int[] rightArr = Arrays.copyOfRange(arr, num, arr.length);System.out.println("split two array: " + Arrays.toString(leftArr) + " And " + Arrays.toString(rightArr));return mergeTwoArray(mergingSort(leftArr), mergingSort(rightArr));      //不断拆分为最小单元，再排序合并
    }private static int[] mergeTwoArray(int[] arr1, int[] arr2){int i = 0, j = 0, k = 0;int[] result = new int[arr1.length + arr2.length];  //申请额外的空间存储合并之后的数组while(i < arr1.length && j < arr2.length){      //选取两个序列中的较小值放入新数组if(arr1[i] <= arr2[j]){result[k++] = arr1[i++];}else{result[k++] = arr2[j++];}}while(i < arr1.length){     //序列1中多余的元素移入新数组result[k++] = arr1[i++];}while(j < arr2.length){     //序列2中多余的元素移入新数组result[k++] = arr2[j++];}System.out.println("Merging: " + Arrays.toString(result));return result;}}