算法-快排

体会轴的概念

先做一个方法,定义一个数组,以最后一个数为轴,把比轴小的数放在轴的左边,比轴大的数放在轴的右边

 1 public static void LastAxleSort(int[]arr,int leftB,int rightB)
 2         {
 3             
 4 
 5             int left = leftB;
 6             int last = rightB;
 7             int right = rightB-1;
 8 
 9 
10             while (left <right)
11             {
12                 while (arr[left] <= arr[last] && left < right)
13                 {
14                     left++;
15                 }
16 
17                 while (arr[right] >= arr[last] && left < right)
18                 {
19                     right--;
20                 }
21 
22                 if (left < right)
23                 {
24                     ExchangeLocation(arr, left, right);
25                 }
26                 else if (left==right)
27                 {
28                     break;
29                 }
30 
31             }
32 
33             if (left<last&& arr[left]>arr[last])
34             {
35                 ExchangeLocation(arr, left, last);
36             }
37 
38         }

扩展为取数组的一部分

 1 public static int LastAxleSortPart1(int[] arr, int leftB, int rightB)
 2         {
 3             
 4 
 5             int left = leftB;
 6             int last = rightB;
 7             int right = rightB - 1;
 8 
 9             int lastValue = arr[last];
10 
11 
12             while (left < right)
13             {
14                 while (arr[left] <= arr[last] && left <= right)
15                 {
16                     left++;
17                 }
18 
19                 while (arr[right] >= arr[last] && left < right)
20                 {
21                     right--;
22                 }
23 
24                 if (left < right)
25                 {
26                     ExchangeLocation(arr, left, right);
27                 }
28                
29 
30             }
31 
32             if (left < last&& arr[left]>arr[last])
33             {
34                 ExchangeLocation(arr, left, last);
35             }
36             //Console.WriteLine();
37             //Console.WriteLine($"左边界:{leftB},右边界:{rightB},排序轴值:{lastValue},返回轴:{left}");
38             //PrintArr(arr);
39             return left;
40 
41         }

递归调用的方法

 1 public static void QuickSortPart(int[] arr,int leftB,int rightB)
 2         {
 3             if (leftB>=rightB)
 4             {
 5                 return;
 6             }
 7             int axle = LastAxleSortPart1(arr, leftB, rightB);
 8 
 9 
10             QuickSortPart(arr, leftB, axle-1);
11             QuickSortPart(arr, axle+1, rightB);
12 
13             //Console.WriteLine($"**");
14 
15         }

posted on 2020-10-17 09:55 雯烈阅读(131) 评论(0) 编辑收藏举报