c - 折半查找(二分法检索)

 1 #include <stdio.h>

 2 

 3 #define LEN 10

 4 

 5 /*

 6 折半查找(二分法检索).

 7 */

 8 

 9 int 

10 index_of(int *a, int k) {

11     int l = 0;

12     int r = LEN -1;

13     int m;

14     while(l <= r) {

15         m = (r + l) >> 1;    //右移(即除以2).

16         if(k == a[m])

17             return m;    //找到,则直接返回下标.

18         else if(k > a[m])

19             l = m + 1;

20         else

21             r = m - 1;    

22     }

23     return -1;    //结束循环后,仍未找到,则表示没有.

24 }

25 

26 

27 int

28 main(void) {

29             // 0  1, 2, 3, 4, 5, 6, 7, 8,  9

30     int a[] = {1, 2, 3, 4, 5, 6, 7, 8, 19, 22};

31     int i = index_of(a, 19);

32     printf("%d\n", i);

33 }