归并排序--JAVA代码实现

import java.util.Arrays;

public class MergeSort {
public static int[] mergeSort(int[] arr,int n) {
if (arr == null || arr.length < 2) {
return arr;
}
process(arr, 0, n - 1);
return arr;

}

public static void process(int[] arr, int left, int right) {
if (left == right) {
return;
}
int mid = (left + right) / 2;
process(arr, left, mid);//分解
process(arr, mid + 1, right);
merge(arr, left, mid, right);//归并
}

public static void merge(int[] arr, int left, int mid, int right) {
int[] help = new int[right - left + 1];
int l = left;
int r = mid + 1;
int index = 0;
while (l <= mid && r <= right) {
if (arr[l] <= arr[r]) {
help[index++] = arr[l++];
} else {
help[index++] = arr[r++];
}
}
while (l <= mid) {
help[index++] = arr[l++];
}
while (r <= right) {
help[index++] = arr[r++];
}
for (int i = 0; i < help.length; i++) {
arr[left + i] = help[i];
}
}
public static void main(String[] args) {
int[] arr = {5,6,1,2,3,4,7,8};
arr = mergeSort(arr, arr.length);
System.out.println(Arrays.toString(arr));
}
}