归并排序

一、问题描述

对数组进行排序

二、方法

  1. 每次对两个小数组进行排序
  2. 将整个大数组一直切分成小数组

三、思想

分治。

四、code

 

 1 package algorithm;
 2 
 3 /**
 4  * Created by adrian.wu on 2019/2/14.
 5  */
 6 public class MergeSort {
 7     public void merge(int[] nums, int s, int m, int e) {
 8         if (s >= e) return;
 9 
10         //new sorted nums
11         int[] nsn = new int[e - s + 1];
12 
13         //as is the start position of s, bs is the start position of b, c is count
14         int c = 0, as = s, bs = m + 1;
15         while (as <= m && bs <= e) {
16             if (nums[as] <= nums[bs]) {
17                 nsn[c++] = nums[as++];
18             } else {
19                 nsn[c++] = nums[bs++];
20             }
21         }
22 
23         while (as <= m) nsn[c++] = nums[as++];
24         while (bs <= e) nsn[c++] = nums[bs++];
25 
26         for (int i = s; i <= e; i++) {
27             nums[i] = nsn[i - s];
28         }
29     }
30 
31     public void mergeSort(int[] nums, int s, int e) {
32         //next mid
33         if (s >= e) return;
34         int m = (e + s) / 2;
35         mergeSort(nums, s, m);
36         mergeSort(nums, m + 1, e);
37         merge(nums, s, m, e);
38     }
39 }

 

posted @ 2019-02-14 17:13  ylxn  阅读(105)  评论(0)  编辑  收藏  举报