Red and Black
Time Limit: 1000MSMemory Limit: 32768KB64bit IO Format: %I64d & %I64u
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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) 
 
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
.#.........
.#.#######.
.#.#.....#.
.#.#.###.#.
.#.#

[email protected]#.#.
.#.#####.#.
.#.......#.
.#########.
...........
11 6
..#..#..#..
..#..#..#..
..#..#..###
..#..#..#@.
..#..#..#..
..#..#..#..
7 7
..#.#..
..#.#..
###.###
[email protected]
###.###
..#.#..
..#.#..
0 0 
 
Sample Output
45
59
6
13 
 
Source

Asia 2004, Ehime (Japan), Japan Domestic

簡單的搜尋問題，根據題意，可以重複行走，求能到達的最多的...的數量，剛開始拿過題來以為是寬搜，因為做了幾個寬搜的題目，形成思維定視了，後來一看到重複行走就想到了深搜。

#include <cstdio>
#include <iostream>
#include <cmath>
#include <queue>
#include <algorithm>

using namespace std;
int dx[4]={-1,0,1,0};
int dy[4]={0,-1,0,1};
int map[40][40];
int m,n;
struct node
{
    int x;
    int y;
    int sept;
};
int sum;
int bfs(int a,int b)
{
    if (map[a][b]=='.')
    {
        map[a][b]='&';
        sum++;
    }

    for (int number1=0;number1<4;number1++)
    {
        int nx=a+dx[number1],ny=b+dy[number1];
        if (map[nx][ny]=='.'&&nx>=0&&nx<n&&ny>=0&&ny<m)
        {
            bfs(nx,ny);
        }
    }
}
int main()
{
    while(scanf("%d %d",&m,&n)!=EOF)
    {
        if (m==0&&n==0)break;
        int i,j;
        getchar();
        for (int number1=0;number1<n;number1++)
        {
            for (int number2=0;number2<m;number2++)
            {
                scanf("%c",&map[number1][number2]);
                if (map[number1][number2]=='@')
                {
                    i=number1;
                    j=number2;
                }
            }
            getchar();
        }
        sum=1;
        bfs(i,j);
        printf("%d\n",sum);
    }
    return 0;
}