题解

#include<bits/stdc++.h>
using namespace std;
int a[10001];
int main()
{
	int n,x;
	cin>>n;
	for(int i=1;i<=n;i++)
	{
		cin>>a[i];
	}
	cin>>x;
	int l=1,r=n,mid=0;
	while(l<=r){
	mid = (l+r)/2;
	if(a[mid]>x)
	{
		r=mid-1;
	}
	else if(a[mid]<x)
	{
		l=mid+1;
	}
	else{
		cout<<mid;
		return 0;
	}
	
	}
	cout<<"-1";
	//cout<<ans;
}