POJ 1979 Red and Black(简单DFS)

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Red and Black

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

最简单常规的深度优先搜索(DFS)题,与POJ2386个题很类似。不再详细解释,直接上代码:
 
#include<iostream>
#include<algorithm>
#include<cstring> using namespace std; char maze[25][25]; bool flag[25][25]; int n,m,dir[4][2] = { {1,0},{-1,0},{0,1},{0,-1} },ans; void dfs(int x, int y) { if (x<=0||x > n ||y<=0|| y > m|| maze[x][y] == \'#\') return; if (flag[x][y])//这个位置未被标记,之前没被走过 { ans++; flag[x][y] = false; } maze[x][y] = \'#\';//对当前位置置换成#,避免下次对这个位置重复DFS for (int i = 0; i < 4; i++)//向四个方向DFS { int nx = x + dir[i][0], ny = y + dir[i][1]; dfs(nx, ny); } return ; } int main() { while (cin >> m >> n,(m||n)) { memset(flag, true, sizeof(flag)); int sx, sy; for (int i = 1; i <= n; i++) for (int j = 1; j <= m; j++) { cin >> maze[i][j]; if (maze[i][j] == \'@\') { sx = i; sy = j; } } ans = 0; dfs(sx, sy); cout << ans << endl; } return 0; }

 

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