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

用DFS做，AC代码如下：

#include
#include
using namespace std;
char s[20][20];
bool flag[20][20];
int width,length,num;
void dfs(int i,int j)
{
	flag[i][j]=true;
	if(i+1=0&&s[i-1][j]=='.'&&flag[i-1][j]==false)
		dfs(i-1,j);
	if(j+1=0&&s[i][j-1]=='.'&&flag[i][j-1]==false)
		dfs(i,j-1);
}
int  main()
{
	int m=0,n=0;
	while((cin>>length>>width)&&width)
	{
		num=0;
		memset(flag,false,sizeof(flag));
		for(int i=0;i>s[i][j];
				if(s[i][j]=='@')
				{
					n=i,m=j;
				}
			}
		}
		dfs(n,m);
		for(int i=0;i