[恢]hdu 1242

2011-12-25 09:54:46

地址：http://acm.hdu.edu.cn/showproblem.php?pid=1242

题意：angel被困在迷宫里，他的朋友们去救。n*m的迷宫，'.'代表路，'#'代表墙，'x'代表守卫，'r'代表朋友，'a'代表ANGEL。求最少时间。

mark：BFS。注意有多个“朋友”，所以从a开始搜。

代码：

# include <stdio.h>
# include <string.h>


int n, m, sx, sy ;
char graph[210][210] ;
int dp[210][210] ;
int q[40010] ;


int bfs()
{
    int front = 0, rear = 0 ;
    int i, x, y, xx, yy, next ;
    int tab[4][2] = {0, 1, 0, -1, 1, 0, -1, 0} ;
    memset (dp, -1, sizeof(dp)) ;
    dp[sx][sy] = 0 ;
    q[rear++] = sx*m+sy ;
    while (front != rear)
    {
        x = q[front] / m ;
        y = q[front++] % m ;
        if (graph[x][y] == 'r') return dp[x][y] ;
        for (i = 0 ; i < 4 ; i++)
        {
            xx = x + tab[i][0] ;
            yy = y + tab[i][1] ;
            if (xx < 0 || xx >= n || yy < 0 || yy >= m)
                continue ;
            if (graph[xx][yy] == '#') continue ;
            if (graph[xx][yy] == 'x') next = 2 ;
            else next =1 ;
            next += dp[x][y] ;
            if (dp[xx][yy]!= -1 &&dp[xx][yy]<=next) continue ;
            dp[xx][yy] = next ;
            q[rear++] = xx * m + yy ;
        }
    }
    return -1 ;
}


int min(int a, int b){return a<b?a:b;}


int main ()
{
    int i, j, ans ;
    while (~scanf ("%d %d%*c", &n, &m))
    {
        for (i = 0 ; i < n ; i++)
            scanf ("%s%*c", graph[i]) ;
        for (i = 0 ; i < n ; i++)
            for (j = 0 ; j < m ; j++)
            {
                if (graph[i][j] == 'a')
                    sx = i, sy = j ;
            }
        ans = bfs () ;
        if (ans == -1)
            puts ("Poor ANGEL has to stay in the prison all his life.") ;
        else printf ("%d\n", ans) ;
    }
    return 0 ;
}