[백준 : 2468] 안전 영역 - JAVA

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.*;

class Dot{
	int x;
	int y;
	public Dot(int x, int y) {
		this.x = x;
		this.y = y;
	}
}
public class Main {
	static int map[][]; // 2차원 미로 배열
	static boolean visit[][]; // 2차원 방문여부 배열
	static ArrayList<Integer> list;
	static int n;
	static int[] dx = {-1,0,1,0};
	static int[] dy = {0,1,0,-1};
	
	public static void dfs(int x, int y, int depth) { //BFS메소드
		visit[x][y] = true;
		
		for(int i = 0 ; i < 4; i++) {
			int nx = x + dx[i];
			int ny = y + dy[i];
			
			if(nx >= 0 && ny >= 0 && nx < n && ny < n) {
				if(map[nx][ny] > depth && !visit[nx][ny])
					dfs(nx,ny,depth);
			}
		}
		
	}
	public static void main(String[] args) throws IOException {
		
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		StringTokenizer st = new StringTokenizer(br.readLine());
		n = Integer.parseInt(st.nextToken());
		 
		map = new int [n][n];
		visit = new boolean[n][n];
		list = new ArrayList<>();
		
		int max = 0, count = 0; 
		for(int i = 0; i < n; i++) {
			st = new StringTokenizer(br.readLine());
			for(int j = 0; j < n; j++) {
				map[i][j] = Integer.parseInt(st.nextToken());
				max = Math.max(max, map[i][j]);
			}
		}
		for(int depth = 0; depth <= max; depth++) {
			count = 0;
			for(int i = 0; i < n; i++) 
				for(int j = 0; j < n; j++) 
					if(map[i][j] > depth && !visit[i][j]) {
						dfs(i,j,depth);
						count++;
					}
			list.add(count);
			for(boolean a[] : visit)
				Arrays.fill(a, false);//visit배열을 다시 false로 채워줌
		}
		int maxCount = Collections.max(list);//가장 큰 값 골라줌
		System.out.println(maxCount);
	}
}