[java 백준] 골드 5/ 11000번 강의실 배정

https://www.acmicpc.net/problem/11000

11000번: 강의실 배정

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.*;
 
class Main {
 
    public static int n;
    public static int ans=0;//답
   
 
    public static class Node implements Comparable<Node>{
        int start;
        int end;
        public Node(int start,int end){
            this.start=start;
            this.end=end;
        }
 
        @Override
        public int compareTo(Node other){
            //시작 시점을 기준으로 정렬
           if(this.start==other.start){
               return this.end-other.end;
           }
            return this.start-other.start;
        }
    }
 
    public static class Node2 implements  Comparable<Node2>{
 
        int node;
        public Node2(int node){
            this.node=node;
        }
        @Override
        public int compareTo(Node2 other){
            return this.node- other.node;
        }
    }
 
 
 
 
    public static void main(String args[]) throws NumberFormatException, IOException {
 
    BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
    n=Integer.parseInt(br.readLine());
    StringTokenizer st;
    PriorityQueue<Node>pqueue=new PriorityQueue<Node>();
    PriorityQueue<Node2>endNodeQueue=new PriorityQueue<Node2>(); //끝값 넣어주는 우선순위 큐
 
    for(int i=0;i<n;i++){
        st=new StringTokenizer(br.readLine());
        int start=Integer.parseInt(st.nextToken());
        int end=Integer.parseInt(st.nextToken());
        pqueue.add(new Node(start,end));
 
 
 
    }
 
    while(!pqueue.isEmpty()){
 
        Node node= pqueue.poll();
 
        int start=node.start;
        int end=node.end;
        if(endNodeQueue.size()==0){
            //empty인 경우 끝값을 넣는다.
 
            endNodeQueue.add(new Node2(end));
            ans++;
 
        }
        else{
            if(endNodeQueue.peek().node>start){
                //이전것의 끝값이 현재의 시작시점보다 크면
 
                endNodeQueue.add(new Node2(end));
                ans++;
 
            }
            else if(endNodeQueue.peek().node<=start){
 
                endNodeQueue.poll();
                endNodeQueue.add(new Node2(end));
 
            }
        }
 
 
 
 
 
    }
 
    System.out.println(ans);
 
 
 
 
 
 
    }
 
}