HDU_1312——二维空间BFS

这题网上都是用DFS做的，我也不知道怎么用BFS做的。。。有个注意点，就是一步也走不动的时候，输出1

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

 

 

Sample Output

45 59 6 13

 1 #include <cstdio>

 2 #include <cstring>

 3 #include <queue>

 4 #define MAX 21

 5 using namespace std;

 6 struct point

 7 {

 8    int x,y;  

 9 }start;

10  

11 int N,M,dir[4][2]={{1,0},{-1,0},{0,1},{0,-1}};

12 char map[MAX][MAX];

13 

14 int Bfs(void);

15 int main()

16 {

17    while(~scanf("%d %d",&M,&N) && N!=0&&M!=0)

18       {

19          memset(map,0,sizeof(map));

20          for(int i=0;i<N;i++)

21             {

22                scanf("%s",map[i]);

23                for(int j=0;j<M;j++)

24                   {

25                      if(map[i][j]=='@')

26                         start.x=i,start.y=j;   

27                   }

28             }

29          int num=Bfs();

30          printf(num==0?"1\n":"%d\n",num);        

31       }

32    return 0;   

33 }

34 

35 int Bfs(void)

36 {

37    int move=0;

38    queue<point>p;

39    p.push(start);

40    point temp,next;

41    while(!p.empty())

42       {

43          temp=p.front();

44          p.pop();

45          for(int i=0,flag=0;i<4;i++)

46             {

47                next.x=temp.x+dir[i][0];

48                next.y=temp.y+dir[i][1];

49                if(next.x>=0&&next.x<N && next.y>=0&&next.y<M && map[next.x][next.y]!='#')

50                   {

51                      map[next.x][next.y]='#';

52                      move++;

53                      p.push(next);

54                   }

55             }

56       }

57    return move;

58 }