Red and Black（DSF）

Problem 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) 

 

 

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

.#.........

.#.#######.

.#.#.....#.

.#.#.###.#.

.#.#[email protected]#.#.

.#.#####.#.

.#.......#.

.#########.

...........

11 6

..#..#..#..

..#..#..#..

..#..#..###

..#..#..#@.

..#..#..#..

..#..#..#..

7 7

..#.#..

..#.#..

###.###

[email protected]

###.###

..#.#..

..#.#..

0 0

 

 

Sample Output

45

59

6

13

 

 

 

很水的一道题，直接DSF便利一遍就好了

 

 

具体代码：

 

#include<iostream>
#include<cstdio>
#include<bits/stdc++.h>
char str[21][21];
int w,h,ans;
int x[4]={0,-1,1,0};
int y[4]={1,0,0,-1};
void DSF(int a,int b)
{
    for(int i=0;i<4;i++)
    {
        if(a>=0&&b>=0&&a<h&&b<w&&str[a+x[i]][b+y[i]]=='.')
        {
            ans++;
            str[a+x[i]][b+y[i]]='#';
            DSF(a+x[i],b+y[i]);
        }
    }
}
int main()
{
    while(scanf("%d%d",&w,&h),w!=0||h!=0)
    {
        int a,b;
        ans=1;
        for(int i=0;i<h;i++)
        {
            scanf("%s",str[i]);
            for(int j=0;j<w;j++)
                if(str[i][j]=='@')a=i,b=j;
        }
        DSF(a,b);
        printf("%d\n",ans);
    }
    return 0;
}