백준 1931번
https://www.acmicpc.net/problem/1931

문제

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생각하기

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• 그리디, 정렬 문제이다.

• PriorityQueue를 활용해서 문제를 해결하였다.

• 정렬조거만 생각하면 사실 어려운 문제는 아님

동작

결과

코드

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import java.io.*;
import java.util.PriorityQueue;
import java.util.StringTokenizer;

public class Main {

    // input
    private static BufferedReader br;

    // variables
    private static int N;
    private static PriorityQueue<Meeting> pQue;
    private static Meeting[] times;

    private static class Meeting implements Comparable<Meeting> {
        int startTime;
        int endTime;

        private Meeting(int startTime, int endTime) {
            this.startTime = startTime;
            this.endTime = endTime;
        }

        @Override
        public int compareTo(Meeting o) {
            if (endTime == o.endTime) {
                return startTime - o.startTime;
            }

            return endTime - o.endTime;
        }

        @Override
        public String toString() {
            return "Meeting{" +
                    "startTime=" + startTime +
                    ", endTime=" + endTime +
                    '}';
        }
    } // End of Meeting class

    public static void main(String[] args) throws IOException {
        br = new BufferedReader(new InputStreamReader(System.in));
        BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(System.out));

        input();

        bw.write(solve());
        bw.close();
    } // End of main()

    private static String solve() {
        StringBuilder sb = new StringBuilder();

        int count = 0;
        int time = 0;
        while (!pQue.isEmpty()) {
            Meeting tmp = pQue.poll();
            if (tmp.startTime >= time) {
                time = tmp.endTime;
                count++;
            }
        }

        sb.append(count);
        return sb.toString();
    } // End of solve()

    private static void input() throws IOException {
        N = Integer.parseInt(br.readLine());
        pQue = new PriorityQueue<>();
        times = new Meeting[N];

        for (int i = 0; i < N; i++) {
            StringTokenizer st = new StringTokenizer(br.readLine());

            int start = Integer.parseInt(st.nextToken());
            int end = Integer.parseInt(st.nextToken());

            pQue.offer(new Meeting(start, end));
        }
    } // End of input()
} // End of Main class