POJ 1979 Red and Black（简单DFS）

#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;
}