poj 1979 Red and Black

Description

There is a rectangular room, covered with square tiles. Each tile is colored either red or black. A man is standing on a black tile. From a tile, he can move to one of four adjacent tiles. But he can't move on red tiles, he can move only on black tiles. 

Write a program to count the number of black tiles which he can reach by repeating the moves described above. 

Input

The input consists of multiple data sets. A data set starts with a line containing two positive integers W and H; W and H are the numbers of tiles in the x- and y- directions, respectively. W and H are not more than 20. 

There are H more lines in the data set, each of which includes W characters. Each character represents the color of a tile as follows. 

'.' - a black tile 
'#' - a red tile 
'@' - a man on a black tile(appears exactly once in a data set) 
The end of the input is indicated by a line consisting of two zeros. 

Output

For each data set, your program should output a line which contains the number of tiles he can reach from the initial tile (including itself).

Sample Input

6 9
....#.
.....#
......
......
......
......
......
#@...#
.#..#.
11 9
.#.........
.#.#######.
.#.#.....#.
.#.#.###.#.
.#.#..@#.#.
.#.#####.#.
.#.......#.
.#########.
...........
11 6
..#..#..#..
..#..#..#..
..#..#..###
..#..#..#@.
..#..#..#..
..#..#..#..
7 7
..#.#..
..#.#..
###.###
...@...
###.###
..#.#..
..#.#..
0 0

Sample Output

45
59
6
13

Source

Japan 2004 Domestic

简单dfs。

代码：

import java.util.*;

public class Main {
    static int w,h,ans;
    static char mp[][];
    static boolean vis[][];
    static int dir[][];
    static void dfs(int x,int y) {
        for(int i = 0;i < 4;i ++) {
            int tx = x + dir[i][0];
            int ty = y + dir[i][1];
            if(tx < 0 || ty < 0 || tx >= h || ty >= w || vis[tx][ty] || mp[tx][ty] == '#')continue;
            vis[tx][ty] = true;
            ans ++;
            dfs(tx,ty);
        }
    }
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int sx = 0,sy = 0;
        dir = new int[][]{{0,1},{1,0},{0,-1},{-1,0}};
        while(true) {
            w = in.nextInt();
            h = in.nextInt();
            if(w == 0 && h == 0)break;
            mp = new char[h][w];
            vis = new boolean[h][w];
            ans = 1;
            for(int i = 0;i < h;i ++) {
                String s = in.next();
                for(int j = 0;j < s.length();j ++) {
                    if(s.charAt(j) == '@') {
                        sx = i;
                        sy = j;
                    }
                    mp[i][j] = s.charAt(j);
                }
            }
            vis[sx][sy] = true;
            dfs(sx,sy);
            System.out.println(ans);
        }
    }
}