hdoj1312Red and Black

Red and Black
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

代码:

#include<stdio.h> #include<string.h> char map[1010][1010]; int vis[1010][1010],n,m,ans,sx,sy; void dfs(int x,int y) { if(x<0||x>=m||y<0||y>=n||vis[x][y]||map[x][y]=='#') return ; vis[x][y]=1; ans++; dfs(x+1,y); dfs(x,y+1); dfs(x-1,y); dfs(x,y-1); } int main() { while(scanf("%d%d",&n,&m)&&n||m) { ans=0; memset(vis,0,sizeof(vis)); memset(map,0,sizeof(map)); for(int i=0;i<m;i++) { scanf("%s",&map[i]); for(int j=0;j<n;j++) { if(map[i][j]=='@') sx=i,sy=j; } } dfs(sx,sy); printf("%d\n",ans); } return 0; }

思路:深搜,dfs,这是第一次接触深搜题,乍一看一点思路也没有啊,然后学长讲完之后也是晕头转向的,迷迷糊糊,晕。然后自己照着代码敲了几遍,记住代码,再根据代码慢慢看懂了,memset(vis,0,sizeof(vis)); memset(map,0,sizeof(map));这个是要记住的,就是把所有的行行竖竖清零,在dfs,bfs里经常用到。然后就是定义dfs了,要记住确定方向dfs(x+1,y);dfs(x,y+1);dfs(x-1,y);dfs(x,y-1);,分别代表上下左右,其次就是找原始的点,然后本题就ac啦,注意不会多多敲几遍哈!!

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