池塘计数java版本

采用dfs会出现

java.lang.StackOverflowError错误

import java.io.*;


public class Main{
    static BufferedReader cin = new BufferedReader(new InputStreamReader(System.in));
    static char[][] arr;
    static int n, m;
    public static void main(String[] args) throws IOException{
        String[] s = cin.readLine().split(" ");
        n = Integer.parseInt(s[0]);
        m = Integer.parseInt(s[1]);
        arr = new char[n][m];
        for (int i = 0; i < n; i++) {
            String str = cin.readLine();
            for (int j = 0; j < m; j++) {
                arr[i][j] = str.charAt(j);
            }
        }
        int res = 0;
        for (int i = 0; i < n; i++) {
            for (int j = 0; j < m; j++){
                if (arr[i][j] == 'W') {
                    dfs(i, j);
                    res++;
                }
            }
        }
        System.out.println(res);
    }

    private static void dfs(int x, int y) {
        arr[x][y] = '.';
        for (int i = -1; i <= 1; i++) {
            for (int j = -1; j <= 1; j++) {
                int a = x + i, b = y + j;
                if (a >= 0 && a < n && b >= 0 && b < m && arr[a][b] == 'W') dfs(a, b);
            }
        }
    }

}

采用宽搜使用队列实现 耗时1569 ms

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

public class Main{
    static BufferedReader cin = new BufferedReader(new InputStreamReader(System.in));
    static char[][] arr;
    static int n, m;

    static class Place {
        int x;
        int y;
        Place(int i, int j) {
            x = i;
            y = j;
        }
    }

    private static void bfs(int x, int y) {
        Queue<Place> q = new LinkedList<>();
        q.offer(new Place(x, y));
        arr[x][y] = '.';
        while (!q.isEmpty()) {
            Place pl = q.poll();
            for (int i = -1; i <= 1; i++) {
                for (int j = -1; j <= 1; j++) {
                    int a = pl.x + i, b = pl.y + j;
                    if (a >= 0 && a < n && b >= 0 && b < m && arr[a][b] == 'W') {
                        q.offer(new Place(a, b));
                        arr[a][b] = '.';
                    }
                }
            }
        }
    }
    public static void main(String[] args) throws IOException{
        String[] s = cin.readLine().split(" ");
        n = Integer.parseInt(s[0]);
        m = Integer.parseInt(s[1]);
        arr = new char[n][m];
        for (int i = 0; i < n; i++) {
            String str = cin.readLine();
            for (int j = 0; j < m; j++) {
                arr[i][j] = str.charAt(j);
            }
        }
        int res = 0;
        for (int i = 0; i < n; i++) {
            for (int j = 0; j < m; j++){
                if (arr[i][j] == 'W') {
                    bfs(i, j);
                    res++;
                }
            }
        }
        System.out.println(res);
    }
}