[11650] 좌표 정렬하기

import java.io.BufferedWriter;
import java.io.IOException;
import java.io.OutputStreamWriter;
import java.util.ArrayList;
import java.util.Collections;
import java.util.HashMap;
import java.util.Scanner;

public class Main {
	static int n,m;
	static int[] arr;
	static BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(System.out));
	public static void main(String[] args) throws IOException {
		Scanner sc = new Scanner(System.in);
		
		HashMap <Integer, ArrayList<Integer>> map = new HashMap<Integer, ArrayList<Integer>>();
		int n = sc.nextInt();
		
		for(int i=0; i<n; i++) {
			int x = sc.nextInt();
			int y = sc.nextInt();
			ArrayList<Integer> list = new ArrayList<Integer>();
			if(map.containsKey(x)) {
				list = map.get(x);
				list.add(y);
				Collections.sort(list);
			}else {
				list.add(y);
			}
			map.put(x, list);
		}
		
		for(int i=-100000; i<=100000; i++) {
			if(map.containsKey(i)) {
				for(int j=0; j<map.get(i).size(); j++) {
					bw.write( i + " " + map.get(i).get(j) + "\n");
				}
			}
		}
		
		bw.flush();
	}
}