Problem:
Problem B: 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

Output for the Sample Input

45
59
6
13

Solution in C++ (judge verdict: Wrong Answer)

#include <iostream>
#include <queue>

using namespace std;

int main(){
    int w,h;
    while(cin >> w >> h && w!=0){
        // int t[100][100];
        int t[h+2][w+2];
        for(int i=0;i<h+2;i++){
            for(int j=0;j<w+2;j++){
                t[i][j] = 0;
            }
        }

        int start;
        for(int i=0;i<h+2;i++){
            for(int j=0;j<w+2;j++){
                if(i==0 || j==0 || i==h+1 || j==w+1)
                    t[i][j]=0;
                else{
                    char tmp; cin >> tmp;
                    if(tmp=='.'){
                        t[i][j] = 1;
                    }
                    else if(tmp=='#'){
                        t[i][j] = 0;
                    }
                    else{
                        t[i][j] = 1;
                        start = i*w+j;
                    }
                }
            }
        }

        //test
        // for(int i=0;i<h+2;i++){
        //     for(int j = 0;j<w+2;j++){
        //         if(j==0)
        //             cout << t[i][j];
        //         else
        //             cout << " " << t[i][j];
        //     }
        //     cout << endl;
        // }

        int ** matrix = new int*[(w+2)*(h+2)];
        for( int i=0; i<(w+2)*(h+2); i++ ) {
            matrix[i] = new int[(w+2)*(h+2)];
        }
        for(int i=0;i<w*h;i++){
            for(int j=0;j<w*h;j++){
                matrix[i][j] = 0;
            }
        }
        for(int i=0;i<h+2;i++){
            for(int j=0;j<w+2;j++){
                int id = i*(w+2)+j;
                if(i==0 || j==0 || i == h+1 || j == w+1 || t[i][j]==0)
                    continue;
                else{
                    if(t[(id-w-2)/(w+2)][(id-w-2)%(w+2)] == 1){
                        matrix[id][id-w-2] = 1;
                    }
                    if(t[(id+w+2)/(w+2)][(id+w+2)/(w+2)] == 1){
                        matrix[id][id+w+2] = 1;
                    }
                    if(t[(id-1)/(w+2)][(id-1)/(w+2)] == 1){
                        matrix[id][id-1] = 1;
                    }
                    if(t[(id+1)/(w+2)][(id+1)/(w+2)] == 1){
                        matrix[id][id+1] = 1;
                    }
                }
            }
        }

        // test
        // for(int i=0;i<(h+2)*(w+2);i++){
        //     for(int j = 0;j<(h+2)*(w+2);j++){
        //         if(j==0)
        //             cout << matrix[i][j];
        //         else
        //             cout << " " << matrix[i][j];
        //     }
        //     cout << endl;
        // }


        int count = 1;
        queue<int> Q;
        int came[(w+2)*(h+2)];
        for(int i=0;i<(w+2)*(h+2);i++){
            came[i] = 0;
        }
        Q.push(start);
        came[start] = 1;
        while(Q.size()!=0){
            int cur = Q.front();
            for(int i=0;i<(w+2)*(h+2);i++){
                if(matrix[cur][i]==1 && came[i] == 0){
                    Q.push(i);
                    came[i] = 1;
                    count++;
                }
            }
            Q.pop();
        }
        cout << count << endl;
        for( int i=0; i<(w+2)*(h+2); i++ ) {
            delete[] matrix[i];
        }
        delete[] matrix;

    }
}