How many tiles

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本文介绍了一种基于递归深度优先搜索的算法，用于计算在一个由黑色和红色方砖构成的矩形房间中，从一个指定的黑色方砖出发可以到达的所有黑色方砖的数量。该算法适用于不超过20×20的迷宫地图，并通过递归方式检查四个相邻的方砖。

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#include<iostream>
#include<cstring>
#include<cstdio>

using namespace std;

char maxr[21][21];
int count=0;

void check(int w,int h,int f,int g){
    if((maxr[f][g]=='.'||maxr[f][g]=='@')&&f>=0&&f<h&&g>=0&&g<w){
        count++;
        maxr[f][g]='#';
        check(w,h,f-1,g);
        check(w,h,f+1,g);
        check(w,h,f,g+1);
        check(w,h,f,g-1);
    }
}


int main()
{
    int w,h;
    while(cin >> w >> h){
        if(w==0&&h==0) break;
        for(int j=0; j < h; j++)
            scanf("%s",&maxr[j]);
        int f,g,k=1;
        for(f=0; f < h; f++){
            for(g=0; g < w; g++){
                if(maxr[f][g]=='@'){
                k=0;
                break;
                }
            }
            if(k==0)break;
        }
        check(w,h,f,g);
        cout << count << endl;
        count=0;
    }
}

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

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6 9
....#.
.....#
......
......
......
......
......
#@...#
.#..#.
11 9
.#.........
.#.#######.
.#.#.....#.
.#.#.###.#.
.#.#..@#.#.
.#.#####.#.
.#.......#.
.#########.
...........

Sample Output

45
59