快速排序

 1 #include<iostream>
 2 #include<cstdlib>
 3 #include<ctime>
 4 using namespace std;
 5 
 6 void swap(int *a, int *b){
 7     int tmp;
 8     tmp = *a;
 9     *a = *b;
10     *b = tmp;
11 }
12 
13 int partition(int A[], int p, int r)
14 {
15     int x = A[r];
16     int i = p-1;
17     int j;
18     for(j=p; j<=r-1; ++j)
19         if(A[j]<=x){
20             i++;
21             swap(A[i], A[j]);
22         }
23     swap(A[i+1], A[r]);
24     return i+1;
25 }
26 
27 int randomized_partition(int A[], int p, int r)
28 {
29     srand(unsigned(time(NULL)));
30     int i = rand()%(r-p) + p;
31     swap(A[r], A[i]);
32     return partition(A, p, r);
33 }
34 
35 void quicksort(int A[], int p, int r)
36 {
37     int q;
38     if(p<r){
39         q = partition(A, p, r);
40         quicksort(A, p, q-1);
41         quicksort(A, q+1, r);
42     }
43 }
44 
45 void randomized_quicksort(int A[], int p, int r)
46 {
47     int q;
48     if(p<r){
49         q = randomized_partition(A, p, r);
50         randomized_quicksort(A, p, q-1);
51         randomized_quicksort(A, q+1, r);
52     }
53 }
54 
55 void print(int A[], int n)
56 {
57     int i;
58     for(i=0; i<n; ++i)
59         cout<<A[i]<<" ";
60 }
61 
62 int main()
63 {
64     int a[]={8, 23, 34, 1231, 9898, 1231, 22, 99};
65     randomized_quicksort(a, 0, 7);
66     print(a, 8);
67     return 0;
68 }