题目链接：http://acm.hdu.edu.cn/showproblem.php?pid=1312
Red and Black
Time Limit: 2000/1000 MS (Java/Others) Memory Limit: 65536/32768 K (Java/Others)
Total Submission(s): 15186 Accepted Submission(s): 9401
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
.#.........
.#.#######.
.#.#.....#.
.#.#.###.#.
.#.#[email protected]#.#.
.#.#####.#.
.#.......#.
.#########.
...........
11 6
..#..#..#..
..#..#..#..
..#..#..###
..#..#..#@.
..#..#..#..
..#..#..#..
7 7
..#.#..
..#.#..
###.###
[email protected]
###.###
..#.#..
..#.#..
0 0
Sample Output
45
59
6
13
1 #include<cstdio>
2 #include<cstring>
3 #include<algorithm>
4 #include<string>
5 using namespace std;
6 #define N 25
7 char mp[N][N];
8 int go[4][2] = {{1,0},{-1,0},{0,-1},{0,1}};
9
10 int n,m;
11 bool ck(int x, int y){
12 if(x<n&&x>=0&&y<m&&y>=0) return true;
13 else return false;
14 }
15 bool vis[N][N];
16 void dfs(int x, int y, int &sum)
17 {
18 vis[x][y] = 1;
19 bool fl = 0;
20 for(int i = 0; i < 4; i++){
21 int xx = x + go[i][0];
22 int yy = y + go[i][1];
23 if(ck(xx,yy)&&!vis[xx][yy]&&mp[xx][yy]==‘.‘){
24 fl = 1;
25 sum = sum+1;
26 dfs(xx,yy,sum);
27 }
28 }
29 if(fl==0) return;
30 }
31 int main()
32 {
33 while(~scanf("%d%d",&m,&n))
34 {
35 int x, y;
36 if(n==0&&m==0) break;
37 getchar();
38 for(int i = 0; i < n; i++){
39 for(int j = 0; j < m; j++){
40 scanf("%c",&mp[i][j]);
41 if(mp[i][j]==‘@‘){ x = i; y = j; }
42 }
43 getchar();
44 }
45 memset(vis,0,sizeof(vis));
46 int sum = 0;
47 dfs(x,y,sum);
48 printf("%d\n",sum+1);
49 }
50 return 0;
51 }