체육복→ 차집합을 구현하는 방법★★

나의 풀이 

import java.util.*;
class Solution {
    public int solution(int n, int[] lost, int[] reserve) {
     Set<Integer> reserveOnly = new HashSet<>();
    for (int r : reserve) {
        reserveOnly.add(r);
    }
    for (int l : lost) {
        reserveOnly.remove(l);
    }

    Set<Integer> lostOnly = new HashSet<>();
    for (int l : lost) {
        lostOnly.add(l);
    }
    for (int r : reserve) {
        lostOnly.remove(r);
    }

    for (int reserveNum : reserveOnly) {
        int front = reserveNum - 1;
        int back = reserveNum + 1;
        if (lostOnly.contains(front)) {
            lostOnly.remove(front);
        } else if (lostOnly.contains(back)) {
            lostOnly.remove(back);
        }
    }

    int answer = n - lostOnly.size();
    return answer;
}
}