[백준] 11650번 좌표 정렬하기 문제! (silver 5

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.util.ArrayList;
import java.util.Collections;
import java.util.StringTokenizer;
public class Main{
	public static void main(String[] args) throws IOException {
		BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
		BufferedWriter bw=new BufferedWriter(new OutputStreamWriter(System.out));
		int n=Integer.parseInt(br.readLine());
		StringTokenizer st;
		ArrayList<Integer>[] num=new ArrayList[200001];
		for(int i=0; i<n; i++) {
			st=new StringTokenizer(br.readLine());
			int x=Integer.parseInt(st.nextToken())+100000;
			int y=Integer.parseInt(st.nextToken());
			
			if(num[x]==null) {
				num[x]=new ArrayList<Integer>();
				num[x].add(y);
			}
			else {
				num[x].add(y);
			}
		}
		for(int i=0; i<num.length; i++) {
			if(num[i]==null) {
				continue;
			}
			else {
				Collections.sort(num[i]);
				for(int j=0; j<num[i].size(); j++) {
					bw.write(i-100000+" "+num[i].get(j)+"\n");
				}		
			}
		}
		bw.flush();
		bw.close();	
	}
}