황민우

import java.util.HashMap; public class Solution { public String solution(String[] participant, String[] completion) { HashMap<String, Integer> map = new HashMap<>(); for (String name : participant) { map.put(name, map.getOrDefault(name, 0) + 1); } for (String name : completion) { if (map.get(name) == 1) map.remove(name); else map.put(name, map.get(name) - 1); } return map.keySet().iterator().next(); } }