#include <stdio.h>
int binary_search(int a[], int k, int s){
    int left = 0;
    int right = s - 1;
    
    while(left <= right){
    int mid = (left + right) / 2;
    if(a[mid] > k){  
        right = mid - 1;
    }
    else if(a[mid] < k){
        left = mid + 1;
    }
    else{
        return mid;
    }
    }
    return -1;
    }

int main(){
    int arr[] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
    int key = 10;
    int sz = sizeof(arr) / sizeof(arr[0]);
    
    int ret = binary_search(arr, key, sz);
    
    if( ret == -1){
       printf("找不到") ;
    }
    else{
        printf("找到了，key的下标是%d\n",ret);
    }
    return 0;
}