POJ 1979 && HDU 1312 Red and Black（DFS）

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

#include <iostream>
#include <cstdio>
using namespace std;
char map[25][25];
int num;
int w,l;//w->width l->lenth
int dx[4] ={0,0,1,-1};
int dy[4] ={1,-1,0,0};
void dfs(int x,int y)
{
int i,xx,yy;
for(i=0;i<4;i++)
{
xx = x+dx[i];
yy = y+dy[i];
if(xx>=0 && xx<w && yy>=0 && yy<l && map[xx][yy]=='.')
{
num++;
map[xx][yy] = '@';
dfs(xx,yy);
}
}
}
int main()
{
//freopen("test.txt","r",stdin);
int i,j;
int sx,sy;
while(cin>>l>>w && l)
{
for(i=0;i<w;i++)
{
for(j=0;j<l;j++)
{
cin>>map[i][j];
if(map[i][j]=='@')
{
sx = i;
sy = j;
}//
}
}
map[sx][sy] = '#';
num = 1;
dfs(sx,sy);
cout << num << endl;
}
//cout << "Hello world!" << endl;
return 0;
}