题解

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