二分搜索

 1 #include<stdio.h>
 2 
 3 int search(int key, int a[], int len);
 4 int main(void)
 5 {
 6     int a[] = { 1,3,6,7,8,9,10,11,13 };
 7     int k = 11;        //需要找的数
 8     int r = search(k, a, sizeof(a) / sizeof(a[0]));
 9 
10     printf("%d", r);
11 
12     return 0;
13 }
14 
15 int search(int key, int a[], int len)
16 {
17     int ret = -1;
18 
19     int left = 0;
20     int right = len - 1;
21     while (left < right)
22     {
23         int mid = (left + right) / 2;
24         if (key == a[mid])
25         {
26             ret = mid;
27             break;                
28         }
29         else if (key < a[mid])
30         {
31             right = mid - 1;
32         }
33         else
34         {
35             left = mid + 1;
36         }
37     }
38 
39     return ret;
40 }