快速排序

1、算法导论描述

　　参见《算法导论》对快速排序的伪代码描述：

　　关键代码：

　　模拟过程表示：

2、C++实现

 1 #include <stdio.h>
 2 #include <stdlib.h>
 3 #include <time.h>
 4 
 5 #define DATA_LEN 20
 6 
 7 void PrintData(int data[], int start_index, int end_index) {
 8     printf("DATA[%d, %d]:", start_index, end_index);
 9     for (int i = 0; i < DATA_LEN; ++i) {
10         printf("%d ", data[i]);
11     }
12     printf("\n");
13 }
14 
15 void Swap(int szData[], int i, int j) {
16     printf("[%d] %d <-> [%d] %d\n", i, szData[i], j, szData[j]);
17     int temp = szData[i];
18     szData[i] = szData[j];
19     szData[j] = temp;
20 }
21 
22 int Partition(int szData[], int startIndex, int endIndex) {
23     PrintData(szData, startIndex, endIndex);
24     int guard = szData[endIndex];
25     int i = startIndex - 1;
26     int j = startIndex;
27     for (; j < endIndex; ++j) {
28         if (szData[j] <= guard) {
29             ++i;
30             Swap(szData, i, j);
31         }
32     }
33 
34     Swap(szData, endIndex, i + 1);
35     return i + 1;
36 }
37 
38 void QuickSort(int szData[], int startIndex, int endIndex) {
39     if (startIndex < endIndex) {
40         int j = Partition(szData, startIndex, endIndex);
41         QuickSort(szData, startIndex, j - 1);
42         QuickSort(szData, j + 1, endIndex);
43     }
44 }
45 
46 int main()
47 {
48     srand((unsigned)time(NULL));
49 
50     int origin_data[DATA_LEN] = { 0 };
51     printf("ORIGIN:");
52     for (int i = 0; i < DATA_LEN; ++i) {
53         origin_data[i] = rand() % 100;
54         printf("%d ", origin_data[i]);
55     }
56     printf("\n");
57 
58     QuickSort(origin_data, 0, DATA_LEN - 1);
59 
60     printf("SORTED:");
61     for (int i = 0; i < DATA_LEN; ++i) {
62         printf("%d ", origin_data[i]);
63     }
64     printf("\n");
65 
66     system("pause");
67     return 0;
68 }

View Code

3、心得

　　单游标一趟遍历，i总指向的是最后一个小于“卫兵”的值所在位置，j不断正向遍历至“卫兵”（最后元素）的倒数第二个。最后交换i+1与“卫兵”就对了！

转载于:https://www.cnblogs.com/kuliuheng/p/10553504.html