353. Design Snake Game

贪食蛇。

GAME OVER有2种情况，1是咬到自己，2是出界。

1）用QUEUE来保留占据的格子，每走一格就添加1个，然后POll()最后一个。 做一个一样的SET来check要走的格子是不是已经在自己身体里。这里需要注意用int[2]来加到SET里是不行的。。开始怀念C的指针了。 我们用一个比较典型的HASH来通过一个整数记录位置。

比如高是4，那么高的INDEX是0-3，不会超过4。对于一个点M,N来说，HASH最后的结果就是m*高 + n，这样不会有collision。。

2）出界比较好判断，知道当前要走的位置就行。。

GAME MOVE ON就是看吃豆(或者吃屎）的问题，用INDEX记录当前的豆，刷新的时候还要判断一次新豆在不在自己身体的SET里。

剩下的就是edge cases，比如要先POLL出再看能不能咬到自己；比如能吃的都吃了该怎么办，题里没说，但是看TEST CASE的意思是吃光了就不吃了。。但是游戏继续。

public class SnakeGame {

    /** Initialize your data structure here.
        @param width - screen width
        @param height - screen height
        @param food - A list of food positions
        E.g food = [[1,1], [1,0]] means the first food is positioned at [1,1], the second is at [1,0]. */

    // boundry
    int w;
    int h;
    // cur location
    int m;
    int n;
    // food
    int index;
    int[][] f;

    Set<Integer> set;
    Queue<Integer> q;

    public SnakeGame(int width, int height, int[][] food)
    {
        m = 0;
        n = 0;
        w = width;
        h = height;
        set = new HashSet<Integer>();
        q = new LinkedList<Integer>();
        set.add(0);
        q.add(0);
        f = food;
        index = 0;

    }

    /** Moves the snake.
        @param direction - 'U' = Up, 'L' = Left, 'R' = Right, 'D' = Down
        @return The game's score after the move. Return -1 if game over.
        Game over when snake crosses the screen boundary or bites its body. */
    public int move(String direction)
    {
        if((direction.equals("R") && n == w-1) || (direction.equals("L") && n == 0) ||
           (direction.equals("U") && m == 0) || (direction.equals("D") && m == h-1)) return -1;

           if(direction.equals("R"))
           {
               n++;
           }
           else if(direction.equals("L"))
           {
               n--;
           }
           else if(direction.equals("U"))
           {
               m--;
           }
           else if(direction.equals("D"))
           {
               m++;
           }

           if(index < f.length && m == f[index][0] && n == f[index][1])
           {
               index++;
               while(index < f.length && eatself(f[index][0],f[index][1])) index++;
           }
           else
           {
               set.remove(q.poll());
               if(eatself(m,n)) return -1;

           }

           int temp = m*w + n;
           q.add(temp);
           set.add(temp);

           return set.size()-1;

    }

    public boolean eatself(int x, int y)
    {
        return set.contains(x*w+y);

    }
}
/*

["SnakeGame","move","move","move","move","move","move"]
[[3,2,[[1,2],[0,1]]],["R"],["D"],["R"],["U"],["L"],["U"]]
["SnakeGame","move","move","move","move","move","move","move","move","move","move","move","move"]
[[3,3,[[2,0],[0,0],[0,2],[2,2]]],["D"],["D"],["R"],["U"],["U"],["L"],["D"],["R"],["R"],["U"],["L"],["D"]]
["SnakeGame","move","move"]
[[2,2,[[0,1]]],["R"],["D"]]
["SnakeGame","move","move","move","move","move","move","move","move","move","move","move","move","move","move","move"]
[[3,3,[[2,0],[0,0],[0,2],[0,1],[2,2],[0,1]]],["D"],["D"],["R"],["U"],["U"],["L"],["D"],["R"],["R"],["U"],["L"],["L"],["D"],["R"],["U"]]
*/

/**
 * Your SnakeGame object will be instantiated and called as such:
 * SnakeGame obj = new SnakeGame(width, height, food);
 * int param_1 = obj.move(direction);
 */

跌跌撞撞，错了好几次……考虑不周。