프로그래머스 - 완주하지 못한 선수

#include <string>
#include <vector>
#include <map>

using namespace std;

string solution(vector<string> participant, vector<string> completion) {
    map<string, int> input;
    map<string, int>::iterator mit;
    vector<string>::iterator it;

    for (it = participant.begin(); it != participant.end(); ++it) {
        input[*it]++;
    }

    for (it = completion.begin(); it != completion.end(); ++it) {
        input[*it]--;
    }

    string answer = "";
    for (mit = input.begin(); mit != input.end(); ++mit) {
        if (mit->second == 1) {
            answer = mit->first;
            break;
        }
    }

    return answer;
}