UVa (BFS) The Monocycle

题目不光要求要到达终点而且要求所走的步数为5的倍数，每个时刻有三个选择，前进，左转弯，右转弯。

所以在vis数组中新增加两个维度即可，vis[x][y][dir][color]表示在(x, y)格子方向朝dir与地面接触的扇形的颜色为color，这个状态是否到达过。

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

 const int maxn = ;
 char maze[maxn][maxn];
 bool vis[maxn][maxn][][];

 struct Node
 {
     int x, y, d, t, step;
     Node(int x=, int y=, int d=, int t=, int step=):x(x), y(y), d(d), t(t), step(step) {}
 }st, ed;

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

 int row, col;

 inline bool in(int x, int y)
 { return x >=  && x < row && y >=  && y < col; }

 int BFS()
 {
     memset(vis, false, sizeof(vis));
     queue<Node> Q;
     Q.push(st);
     vis[st.x][st.y][][] = true;
     while(!Q.empty())
     {
         Node now = Q.front(); Q.pop();
         if(now.x == ed.x && now.y == ed.y && now.step %  == )
             return now.t;

         int d = now.d;
         int x = now.x + dx[d];
         int y = now.y + dy[d];
         int t = now.t + ;
         int step = now.step + ;
         if(in(x, y) && maze[x][y] != '#' && !vis[x][y][d][step%])
         {
             Q.push(Node(x, y, d, t, step));
             vis[x][y][d][step%] = true;
         }

         for(int i = ; i <= ; i += )
         {
             x = now.x; y = now.y;
             d = (now.d + i) % ;
             t = now.t + ;
             step = now.step;
             if(!vis[x][y][d][step%])
             {
                 Q.push(Node(x, y, d, t, step));
                 vis[x][y][d][step%] = true;
             }
         }
     }
     return -;
 }

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

     int kase = ;
     while(scanf("%d%d", &row, &col) == )
     {
         if(row ==  && col == ) break;

         if(kase++ > ) puts("");
         printf("Case #%d\n", kase);

         if(row ==  && col == ) break;
         for(int i = ; i < row; i++) scanf("%s", maze[i]);
         for(int i = ; i < row; i++)
             for(int j = ; j < col; j++)
             {
                 if(maze[i][j] == 'S') st = Node(i, j, , , );
                 if(maze[i][j] == 'T') ed = Node(i, j);
             }

         int ans = BFS();
         if(ans >= ) printf("minimum time = %d sec\n", ans);
         else puts("destination not reachable");
     }

     return ;
 }

代码君