POJ 2386 Lake Counting【DFS】

野性酷女 2022-06-17 00:37 124阅读 0赞

# **Lake Counting** #

**Description**  
Due to recent rains, water has pooled in various places in Farmer John’s field, which is represented by a rectangle of N x M (1 <= N <= 100; 1 <= M <= 100) squares. Each square contains either water (‘W’) or dry land (‘.’). Farmer John would like to figure out how many ponds have formed in his field. A pond is a connected set of squares with water in them, where a square is considered adjacent to all eight of its neighbors.

Given a diagram of Farmer John’s field, determine how many ponds he has.

**Input**

*  Line 1: Two space-separated integers: N and M
 *  Lines 2..N+1: M characters per line representing one row of Farmer John’s field. Each character is either ‘W’ or ‘.’. The characters do not have spaces between them.

**Output**

*  Line 1: The number of ponds in Farmer John’s field.

**Sample Input**

> 10 12  
> W……..WW.  
> .WWW…..WWW  
> ….WW…WW.  
> ………WW.  
> ………W..  
> ..W……W..  
> .W.W…..WW.  
> W.W.W…..W.  
> .W.W……W.  
> ..W…….W.

**Sample Output**

> 3

**Hint**  
OUTPUT DETAILS:  
There are three ponds: one in the upper left, one in the lower left,and one along the right side.

**Source**  
USACO 2004 November

**Code**

import java.util.Scanner;
    
    public class Main { 
        public static void main(String[] args) {
            Scanner sc = new Scanner(System.in);
            int N = sc.nextInt();
            int M = sc.nextInt();
            char[][] field= new char[N][M];
            for(int i=0;i<N;i++){
                String temp = sc.next();
                field[i] = temp.toCharArray();
            }
    
            int count = 0;
            for(int i=0;i<N;i++)
                for(int j=0;j<M;j++)
                    if(field[i][j] == 'W'){
                        dfs(i,j,field,N,M);
                        count++;
                    }
            System.out.println(count);
        }
    
        private static void dfs(int x, int y, char[][] field,int N,int M) {
            field[x][y] = '.';
            for(int i=-1;i<=1;i++)
                for(int j=-1;j<=1;j++){
                    int dx = x+i;
                    int dy = y+j;
                    if(dx>=0&&dx<N&&dy>=0&&dy<M&&field[dx][dy] == 'W')
                        dfs(dx, dy, field,N,M);
                }
        }
    }