A

                                                  A - Red and Black

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

4559613

代码：

#include<iostream>using namespace std;int mov[4][2]={-1,0,1,0,0,-1,0,1};int sum,w,h;char s[20][20];void dfs(int x,int y){    sum++;    s[x][y]='#';    for(int i=0;i<4;i++)    {        int tx=x+mov[i][0];        int ty=y+mov[i][1];        //cout<<tx<<" "<<ty<<endl;        if(s[tx][ty]=='.'&&tx>=0&&tx<h&&ty>=0&&ty<w)        {            //cout<<tx<<" "<<ty<<" "<<sum<<endl;            dfs(tx,ty);        }    }}int main(){    int x,y,i,j;    while(cin>>w>>h&&w!=0&&h!=0)    {        for(i=0;i<h;i++)        {            for(j=0;j<w;j++)            {                cin>>s[i][j];                if(s[i][j]=='@')                {                    x=i;                    y=j;                }            }        }        //cout<<x<<" "<<y<<endl;        sum=0;        dfs(x,y);        cout<<sum<<endl;    }    return 0;}

WA了两次，都是运行没错，唉，细节问题啊。注意tx、ty也得>=0！！！