题解

#include <bits/stdc++.h>
using namespace std;
int a[105];
int n,m;
int binSearch(int x){
    int l=1,r=n;
    while(l<=r){
        int mid=(l+r)/2;
        if(a[mid]>x){
            r=mid-1;
            
        }else if(a[mid]<x){
            l=mid+1;
        }else{
            return mid;
        }
    }
    return -1;
}
int main(){
    cin>>n;
    for(int i=1;i<=n;i++)cin>>a[i];
    cin>>m;
    cout<<binSearch(m);
    return 0;
}