题解

#include<bits/stdc++.h>
using namespace std;
int main()
{
    string a,b;
    int T;
    cin>>a;
    cin>>T;
    vector<int>n;
    stringstream str(a);
    while(getline(str,b,','))
        {
            n.push_back(stoi(b));
        }
    int L=0,R=n.size()-1,M;
	bool f=false;
	while(L<=R)
	{
		M=L+(R-L)/2;
		if(n[M]==T)
		{
			f=true;
			cout<<M;
			break;
		}
		else if(n[M]<T)L=M+1;
		else R=M-1;
	}
	if(f==false)
	{
		cout<<"-1";
	}
    return 0;
}