题解 | 特殊城市

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

int main() {
    int count;
    cin >> count;
    unordered_map<string,vector<string>> stateMap;
    int res =0;
    while(count--){
        string city,state;
        cin >> city >> state;
        if(city.substr(0,2) == state) continue;
        if(stateMap.find(city.substr(0,2)) != stateMap.end()){
            for(auto i : stateMap[city.substr(0,2)]){
                if(i.substr(0,2) == state){
                    res++;
                }
            }
        }
        stateMap[state].push_back(city);
        
    }
    cout << res <<endl;

}
// 64 位输出请用 printf("%lld")