백준 2667번(Java)

import java.util.*;
import java.io.*;

public class Main {
	
	static int[][] danji;
	static boolean[][] visited;
	static int[] dx = {0,0,-1,1};
	static int[] dy = {-1,1,0,0};
	static List<Integer> result;
	static int cnt, N;

	public static void main(String[] args) throws IOException{
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(System.out));
		
		result = new LinkedList<>(); 
		N = Integer.parseInt(br.readLine());
		danji = new int[N][N];
		visited = new boolean[N][N]; //단지에 속해있는지
		cnt = 1; //기준이 아파트(단지로 묶일 첫 아파트)가 포함될 때니 1로 초기화
		
		for(int i=0;i<N;i++) {
			String str = br.readLine();
			for(int j=0;j<N;j++) {
				danji[i][j] = str.charAt(j)-'0';
			}
		}
		
		
		for(int x=0;x<N;x++) {
			for(int y=0;y<N;y++) {
				if(danji[x][y]==1 && !visited[x][y]) {
					dfs(x,y);
					result.add(cnt);
					cnt = 1;
				}
			}
		}
		
		Collections.sort(result);
		
		bw.write(result.size()+"\n");
		for(int r : result) bw.write(r+"\n");
		bw.flush();
		bw.close();

	}
	
	public static void dfs(int x, int y) {
		visited[x][y] = true;
		
		for(int i=0;i<4;i++) {
			int nx = dx[i]+x;
			int ny = dy[i]+y;
			
			if(nx>=0 && ny>=0 && nx<N && ny<N && !visited[nx][ny] && danji[nx][ny]==1) {
				cnt++;
				dfs(nx,ny);
			}
		}
	}
}