완주하지 못한 선수

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

string solution(vector<string> participant, vector<string> completion) {
    unordered_map<string,int> map;
    
    for(string name:participant){
        map[name]++;
    } 
    for(string name:completion){
        map[name]--;
    }
    for(auto answer:map){
        if(answer.second >0)
            return answer.first;
    }
}