[알고리즘문제풀기] 완주하지 못한 선수

문제

내가 작성한 오답

class Solution {
    public String solution(String[] participant, String[] completion) {
        String answer = "";
        for(String s:completion){
            for(int i=0; i<participant.length; i++){
                if(participant[i].equals(s)) {
                    participant[i] = "";
                    break;
                }
            }
        }
        for(String s:participant){
            if(!s.isEmpty()) return s;
        }
        return answer;
    }
}

내가 작성한 정답

// Array 이용
import java.util.*;
class Solution {
    public String solution(String[] participant, String[] completion) {
        String answer = "";
        Arrays.sort(participant);
        Arrays.sort(completion);
        for(int i=0; i<completion.length; i++){
            if(!participant[i].equals(completion[i])) return participant[i];
        }
        return participant[participant.length-1];
    }
}

// HashMap이용
import java.util.*;
class Solution {
    public String solution(String[] participant, String[] completion) {
        Map<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(Map.Entry<String,Integer> e: map.entrySet()){
            if(e.getValue()==1) return e.getKey();
        }
        return "";
    }
}

다른 사람들의 정답

import java.util.Arrays;
import java.util.Iterator;
import java.util.Map;
import java.util.function.Function;
import java.util.stream.Collectors;

class Solution {
    public String solution(String[] participant, String[] completion) {

        Map<String, Long> participantMap = Arrays.asList(participant).stream()
                .collect(Collectors.groupingBy(Function.identity(), Collectors.counting()));

        for(String name : completion) {

            Long value = participantMap.get(name) - 1L;

            if(value == 0L) {
                participantMap.remove(name);
            } else {
                participantMap.put(name, value);
            }
        }

        return participantMap.keySet().iterator().next();
    }
}