二分查找

对有序数组{2、11、15、19、30、32、61、72、88、90、96}进行二分查找，则成功找到15需比较()次：
A 3 B 4 C 2 D 5

#include <stdio.h>
#include <stdlib.h>

int binary_search(int* a, int len, int goal)
{
    int low = 0;
    int high = len - 1;
    while(low <= high)
    {
        int middle = (low + high)/2;
        if(a[middle] == goal)
            return middle;
        //在左半边
        else if(a[middle] > goal)
            high = middle - 1;
        //在右半边
        else
            low = middle + 1;
    }
    //没找到
    return -1;
}

int main(void){
    int a[11] = {2,11,15,19,30,32,61,72,88,90,96};
    printf("%d
", binary_search(a, 11, 15));
    return 0;
}

答案是2次