一、解题思路

采用unordered_map建立起QQ号和pwd的映射，仅此而已

二、解题代码

#include <iostream>
#include <string>
#include <unordered_map>
using namespace std;

int main(){
   
    int N;
    cin >> N;
    unordered_map<string, string> ump;
    for(int i = 0; i < N; i++){
   
        char cmd;
        string id, pwd;
        cin >> cmd >> id >> pwd;
        if(cmd == 'L'){
   
            if(ump.find(id) == ump.end())    cout << "ERROR: Not Exist" << endl;
            else if(ump[id] == pwd)    cout << "Login: OK" << endl;
            else    cout << "ERROR: Wrong PW" << endl;
        }
        else if(cmd == 'N'){
   
            if(ump.find(id) != ump.end())    cout << "ERROR: Exist" << endl;
            else {
   
                ump[id] = pwd;
                cout << "New: OK" << endl;
            }
        }
    }
    return 0;
}

三、运行结果