백준 - 2468

https://www.acmicpc.net/problem/2468

2468번: 안전 영역

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

public class Main {
    static int[][] arr;
    static boolean[][] visited;
    static int N;
    static int[] dx = {-1, 1, 0, 0};
    static int[] dy = {0, 0, -1, 1};
    static int[] result;

    public static void main(String[] args) throws NumberFormatException, IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        StringTokenizer st;

        N = Integer.parseInt(br.readLine());
        arr = new int[N][N];
        int max_len = 0;

        for (int i = 0; i < arr.length; i++) {
            st = new StringTokenizer(br.readLine());
            for (int j = 0; j < arr.length; j++) {
                arr[i][j] = Integer.parseInt(st.nextToken());
                if (max_len < arr[i][j]) max_len = arr[i][j];
            }
        }

        result = new int[max_len];

        for (int k = 0; k <= max_len; k++) {
            visited = new boolean[N][N];
            for (int i = 0; i < arr.length; i++) {
                for (int j = 0; j < arr.length; j++) {
                    if (arr[i][j] > k && !visited[i][j]) {
                        result[k]++;
                        dfs(i, j, k);
                    }
                }
            }
        }

        int answer = 0;
        for (int j : result) {
            if (answer < j) answer = j;
        }

        System.out.println(answer);
        br.close();
    }

    public static void dfs(int y, int x, int depth) {
        visited[y][x] = true;

        for (int i = 0; i < 4; i++) {
            int xx = x + dx[i];
            int yy = y + dy[i];

            if (xx < 0 || xx >= N || yy < 0 || yy >= N) continue;
            if (arr[yy][xx] > depth && !visited[yy][xx]) {
                dfs(yy, xx, depth);
            }
        }
    }
}