MergeSort
归并排序(MERGE-SORT)是利用归并的思想实现的排序方法,该算法采用经典的分治(divide-and-conquer)策略(分治法将问题分(divide)成一些小的问题然后递归求解,而治(conquer)的阶段则将分的阶段得到的各答案”修补”在一起,即分而治之)。
package com.sort;
import java.util.Arrays;
public class Code_05_MergeSort {
public static void MergeSort(int[] arr) {
if (arr == null || arr.length < 2) {
return;
}
sortProcess(arr, 0, arr.length - 1);
}
public static void sortProcess(int[] arr, int L, int R) {
if (L == R) {
return;
}
int mid = (L + R) / 2;
sortProcess(arr, L, mid);
sortProcess(arr, mid + 1, R);
merge(arr, L, mid, R);
}
// 整体有序
public static void merge(int[] arr, int L, int mid, int R) {
int[] help = new int[R - L + 1];
int i = 0;
int p1 = L;
int p2 = mid + 1;
while (p1 <= mid && p2 <= R) {
help[i++] = arr[p1] < arr[p2] ? arr[p1++] : arr[p2++];
}
while (p1 <= mid) {
help[i++] = arr[p1++];
}
while (p2 <= R) {
help[i++] = arr[p2++];
}
for (i = 0; i < help.length; i++) {
arr[L + i] = help[i];
}
}
public static void main(String[] args) {
int []arr = {9,8,7,6,5,4,3,2,1};
MergeSort(arr);
System.out.println(Arrays.toString(arr));
}
}