算法导论：快速排序和插入排序

代码实现

 1 #ifndef _SORT_H
 2 #define _SORT_H
 3 
 4 // goal: quicksort and insertsort
 5 // time: 12/2/2014
 6 // author: zrss
 7 // reference: introduction to algorithms
 8 
 9 class Sort {
10 public:
11     void quickSort(int A[], int p, int r);
12     void insertSort(int A[], int p, int r);
13 
14 private:
15     int partition(int A[], int p, int r); // for quickSort
16 };
17 
18 int Sort::partition(int A[], int p, int r) {
19     int x = A[r]; // use A[r] as pivot node
20     
21     int i = p - 1; // point to left part
22 
23     // divide A array to three part
24     // A[p - i] <= x
25     // A[(i + 1) - j] > x
26     // A[(j + 1) - r) unknown
27     for (int j = p; j < r; ++j) {
28         if (A[j] <= x) {
29             ++i;
30             if (i != j) { // swap A[i] and A[j]
31                 int temp = A[i];
32                 A[i] = A[j];
33                 A[j] = temp;
34             }
35         }
36     }
37 
38     // exchange A[i + 1] and A[r]
39     A[r] = A[i + 1];
40     A[i + 1] = x;
41 
42     return (i + 1);
43 }
44 
45 void Sort::quickSort(int A[], int p, int r) {
46     if (p < r) {
47         int q = partition(A, p, r);
48         quickSort(A, p, q - 1);
49         quickSort(A, q + 1, r);
50     }
51 }
52 
53 void Sort::insertSort(int A[], int p, int r) {
54     for (int j = p + 1; j <= r; ++j) {
55         int key = A[j];
56         int i = j - 1;
57         while (i >= p && A[i] > key) { // move backward
58             A[i + 1] = A[i];
59             --i;
60         }
61 
62         if (i + 1 != j) { // insert A[j] to right position
63             A[i + 1] = key;
64         }
65     }
66 }
67 
68 
69 #endif

插入排序与快速排序运行时间比较

随机产生100,000个int测试数据

 1 #include <cstdio>
 2 #include <cstdlib>
 3 #include "windows.h"
 4 #include "sort.h"
 5 
 6 int main(void) {
 7     const int length = 100000;
 8     int number[length];
 9 
10     for (int i = 0; i < length; ++i) {
11         number[i] = rand();
12     }
13 
14     Sort sort;
15 
16     DWORD st = GetTickCount();
17 
18     sort.insertSort(number, 0, length - 1);
19     //sort.quickSort(number, 0, length - 1);
20 
21     DWORD ed = GetTickCount();
22 
23     printf("InsertSort use time: %dms\n", ed - st);
24     //printf("QuickSort use time: %dms\n", ed - st);
25 
26     system("pause");
27     return 0;
28 }

InsertSort use time: 2200ms

QuickSort use time: 0ms

系统信息

System: Windows 7 professional Service Pack 1

CPU: Intel(R) Pentium(R) Dual CPU E2220 @ 2.40GHz 2.40GHz

Memory: 3.00 GB

结论

在输入为100, 000数量级上，且输入的数据为随机值时，快速排序的效率优于插入排序

 

posted @ 2014-12-02 12:17  哲人善思  阅读(1883)  评论(1)  编辑  收藏  举报