Red and Black

Time Limit: 2000/1000 MS (Java/Others) Memory Limit: 65536/32768 K (Java/Others)
Total Submission(s): 8911 Accepted Submission(s): 5535


Problem 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
.#.........
.#.#######.
.#.#.....#.
.#.#.###.#.
.#.#..@#.#.
.#.#####.#.
.#.......#.
.#########.
...........
11 6
..#..#..#..
..#..#..#..
..#..#..###
..#..#..#@.
..#..#..#..
..#..#..#..
7 7
..#.#..
..#.#..
###.###
...@...
###.###
..#.#..
..#.#..
0 0
此題中@也算一個可以走位置所以答案要加1，搜索時注意標記走過的點的位置以免重復計算 還有邊界也要注意 

#include
#include
using namespace std;
int ans,n,m;
int dy[4]={0,1,0,-1};
int dx[4]={1,0,-1,0};
char a[1005][1005],b[1005][1005];
void dfs(int x,int y)
{
    int xx,yy,i;
    for(i=0;i<4;i++)
    {
        xx=x+dx[i]; //此處注意不能直接用x+=d[x];否則回溯時不會回到x的初始值
        yy=y+dy[i];
        if(a[xx][yy]=='.'&&xx>=0&&xx=0&&yy>n>>m,m&&n)
    {
        ans=0;
        for(i=0;i>a[i][j];
        for(i=0;i