POJ 1979 Red and Black

Red and Black

Time Limit: 1000MS		Memory Limit: 30000K
Total Submissions: 33405		Accepted: 18176

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) 
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

45
59
6
13

Source

Japan 2004 Domestic

#include<iostream>
#include<cstring>
#include<cstdio>
using namespace std;
char map[25][25];
bool vis[25][25]; 
int n,m,sx,sy,sum;
int dx[]={0,0,1,-1};
int dy[]={1,-1,0,0};
void Dfs(int x,int y){
    sum++;vis[x][y]=true;
    for(int i=0;i<4;i++){
        int nx=x+dx[i],ny=y+dy[i];
        if(nx<=n&&nx>=1&&ny<=m&&ny>=1&&
            map[nx][ny]=='.'&&!vis[nx][ny])
        Dfs(nx,ny);
    }
}
void init(){
    memset(vis,false,sizeof(vis));
    memset(map,'0',sizeof(map));
    sum=0;
}
int main()
{
    while(1){
        scanf("%d%d",&m,&n);
        if(n==0&&m==0) break;
        init();
        for(int i=1;i<=n;i++)
          for(int j=1;j<=m;j++){
              cin>>map[i][j];
              if(map[i][j]=='@') sx=i,sy=j;
          }
        Dfs(sx,sy);
        printf("%d
",sum);
    }
    return 0;
}