题解

#include<iostream>
using  namespace std;
int main(){
    int n;
    cin>>n;
    int a[n+10];
    for(int i=1;i<=n;i++){
        cin>>a[i];
    }
    int x;
    cin>>x;
    int l=1,r=n;
    while(l<=r){
        int mid=(l+r)/2;
        if(a[mid]==x){
            cout<<mid;
            return 0;
        }else if(a[mid]<x){
            l=mid+1;
        }else{
            r=mid-1;
        }
    }
    cout<<-1;
    return 0;
}