二分搜索

#include<stdio.h>

int search(int key, int a[], int len);
int main(void)
{
    int a[] = { 1,3,6,7,8,9,10,11,13 };
    int k = 11;        //需要找的数
    int r = search(k, a, sizeof(a) / sizeof(a[0]));

    printf("%d", r);

    return 0;
}

int search(int key, int a[], int len)
{
    int ret = -1;

    int left = 0;
    int right = len - 1;
    while (left < right)
    {
        int mid = (left + right) / 2;
        if (key == a[mid])
        {
            ret = mid;
            break;                
        }
        else if (key < a[mid])
        {
            right = mid - 1;
        }
        else
        {
            left = mid + 1;
        }
    }

    return ret;
}