#include<iostream>
using namespace std;


int main() {
 int arr[5] = {1,2,3,4,5};
 int item = 2;

 int arrayLen = sizeof(arr)/sizeof(arr[0]);
 int low = 0;
 int high = arrayLen - 1;
 int result = -1;

 while (low <= high) {
 int mid = (low + high) / 2;
 if (item == arr[mid]){
 cout<<mid<<endl; //输出的结果是下标
 return 0;
 }
 else if (item < arr[mid])
 high = mid - 1;
 else 
 low = mid + 1;
 }

 cout<<result<<endl;
 return 0;
}