HDU1312 / POJ1979 / ZOJ2165 Red and Black（红与黑） 解题报告

题目链接：HDU1312 / POJ1979 / ZOJ2165 Red and Black（红与黑）

Red and Black

Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 65536/32768 K (Java/Others)
Total Submission(s): 9902    Accepted Submission(s): 6158

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

 

Source

Asia 2004, Ehime (Japan), Japan Domestic

题意：

有一个长方形的房间布满了正方形的瓷砖，瓷砖要么红色要么黑色。一男子站在当中一块黑色瓷砖上，可向上下左右四个方向移动。但不能移动到红色瓷砖上，问他可到达的黑色瓷砖数量。

分析：

DFS搜索。

代码：

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;

int dir[4][2] = {{-1, 0},{0, 1},{1, 0},{0, -1}};
int cnt, W, H;
char mp[21][21];
bool vis[21][21];
void dfs(int x, int y)
{
    vis[x][y] = true;
    for(int i = 0; i < 4; i++)
    {
        int tx = x + dir[i][0];
        int ty = y + dir[i][1];
        if(tx >= 1 && tx <= H && ty >= 1 && ty <= W && !vis[tx][ty] && mp[tx][ty] == '.')
        {
            cnt++;
            dfs(tx, ty);
        }
    }
}
int main()
{
    char c;
    int x, y;
    while(scanf("%d%d", &W, &H), W, H)
    {
        scanf("%c", &c);
        for(int i = 1; i <= H; i++)
        {
            for(int j = 1; j <= W; j++)
            {
                scanf("%c", &mp[i][j]);
                if(mp[i][j] == '@')
                {
                    x = i;
                    y = j;
                }
            }
            scanf("%c", &c);
        }
        cnt = 1;
        memset(vis, false, sizeof(vis));
        dfs(x, y);
        printf("%d\n", cnt);
    }
    return 0;
}