[프로그래머스] 완주하지 못한 학생

import java.util.*;
class Solution {
    public String solution(String[] participant, String[] completion) {
        String answer = "";
        HashMap<String, Integer> map = new HashMap<>();
        
        for(String s: participant){
            map.put(s, map.getOrDefault(s, 0)+1);
        }
        
        for(String s: completion){
            map.put(s, map.get(s)-1);
        }
        
        for(String player: map.keySet()){
            if(map.get(player)!=0){
                answer = player;
                break;
            }
        }
        
        return answer;

    }
}