hdu 1242 找到朋友最短的时间 (BFS+优先队列)

找到朋友的最短时间

Sample Input
7 8
#.#####. //#不能走 a起点 x守卫 r朋友
#.a#..r. //r可能不止一个
#..#x...
..#..#.#
#...##..
.#......
........

Sample Output
13

bfs+优先队列

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

 int n, m;
 char map[][];
 int sx, sy;
 bool flag;

 struct node
 {
     int x , y , step ;
     bool operator <(const node &t) const
     {
         return step > t.step ;
     }
 };

 int dx[] = {,,,-} ;
 int dy[] = {,-,,} ;

 void bfs()
 {
     node now , t ;
     int i , fx ,fy ;
     priority_queue<node> q ;
     now.x = sx ;
     now.y = sy ;
     now.step =  ;
     q.push(now) ;
     map[sx][sy] = '#' ;
     while(!q.empty())
     {
         now = q.top() ;
         q.pop() ;
         for (i =  ; i <  ; i++)
         {
             fx = now.x + dx[i] ;
             fy = now.y + dy[i] ;
             if (fx< || fy< || fx >=n || fy >=m ||map[fx][fy] == '#')
                 continue ;
             if (map[fx][fy] == 'r')
             {
                 printf("%d\n" , now.step+) ;
                 flag =  ;
                 return ;
             }
             if (map[fx][fy] == 'x')
             {
                 t.x = fx ;
                 t.y = fy ;
                 t.step = now.step +  ;
                 q.push(t) ;
             }
             else
             {
                 t.x = fx ;
                 t.y = fy ;
                 t.step = now.step +  ;
                 q.push(t) ;
             }
             map[fx][fy] = '#' ;

         }
     }

 }

 int main()
 {
   //  freopen("in.txt","r",stdin) ;
     while (scanf("%d %d" , &n , &m) !=EOF)
     {
         int i , j ;
         for (i =  ; i < n ; i++)
         {
             for (j =  ; j < m ; j++)
             {
                 cin>>map[i][j] ;
                 if (map[i][j] == 'a')
                 {
                     sx = i ;
                     sy = j ;
                 }
             }
         }
         flag =  ;
         bfs() ;
         if (!flag)
             printf("Poor ANGEL has to stay in the prison all his life.\n") ;
     }

     return  ;
 }

dfs

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

 char map[][] ;
 bool visit[][] ;

 int n , m ;
 int MIN ;

 void dfs(int x , int y , int sum)
 {
     if (x< || y< || x>= n || y>= m)
         return ;
     if (map[x][y] == '#')
         return ;
     if (sum >= MIN)
         return ;
     if (visit[x][y] == )
         return ;
     if (map[x][y] == 'r')
     {
         if (sum < MIN)
             MIN = sum ;
         return ;
     }
     if (map[x][y] == 'x')
         sum++ ;
     visit[x][y] =  ;
     dfs(x+,y,sum+) ;
     dfs(x-,y,sum+) ;
     dfs(x,y+,sum+) ;
     dfs(x,y-,sum+) ;
     visit[x][y] =  ;
 }

 int main()
 {
    // freopen("in.txt","r",stdin) ;

    while (scanf("%d %d" , &n , &m) !=EOF)
    {
        if (n ==  && m == )
           break ;
        memset(visit , ,sizeof(visit)) ;
        int i , j ;
        int bx , by ;
        int sum =  ;

        for (i =  ; i < n ; i++)
        {
            for (j =  ; j < m ; j++)
           {
               cin>>map[i][j];
               if (map[i][j] == 'a')
               {
                   bx = i ;
                   by = j ;

               }
           }

        }

        MIN = INT_MAX ;
        dfs(bx,by,sum) ;
        if (MIN != INT_MAX)
          printf("%d\n" , MIN) ;
        else
          printf("Poor ANGEL has to stay in the prison all his life.\n") ;

    }

     return ;
 }