Design a Snake game that is played on a device with screen size = width x height. Play the game online if you are not familiar with the game.
The snake is initially positioned at the top left corner (0,0) with length = 1 unit.
You are given a list of food's positions in row-column order. When a snake eats the food, its length and the game's score both increase by 1.
Each food appears one by one on the screen. For example, the second food will not appear until the first food was eaten by the snake.
When a food does appear on the screen, it is guaranteed that it will not appear on a block occupied by the snake.

Example:

Given width = 3, height = 2, and food = [[1,2],[0,1]].Snake snake = new Snake(width, height, food);

Initially the snake appears at position (0,0) and the food at (1,2).

|S| | |
| | |F|

snake.move("R"); -> Returns 0

| |S| |
| | |F|

snake.move("D"); -> Returns 0

| | | |
| |S|F|

snake.move("R"); -> Returns 1 (Snake eats the first food and right after that, the second food appears at (0,1) )

| |F| |
| |S|S|

snake.move("U"); -> Returns 1

| |F|S|
| | |S|

snake.move("L"); -> Returns 2 (Snake eats the second food)

| |S|S|
| | |S|

snake.move("U"); -> Returns -1 (Game over because snake collides with border)

一刷
题解：
首先将一个二维数组flat为一维，用一个linkedlist表示蛇的身体，每移动一格， add在头部，移去尾部。一个set存储蛇身体的各个位置，如果duplicate, 表示撞到了自己，游戏结束。

class SnakeGame {
    
    Set<Integer> set;
    Deque<Integer> body;
    int score;
    int[][] food;
    int foodIndex =0;
    int width;
    int height;

    /** 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]. */
    public SnakeGame(int width, int height, int[][] food) {
        this.width = width;
        this.height = height;
        this.food = food;
        set = new HashSet<>();
        set.add(0);//initially at [0][0]
        body = new LinkedList<>();
        body.offerLast(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) {
         //case 0: game already over: do nothing
        if(score == -1) return -1;
        
        int rowHead = body.peekFirst() / width;
        int colHead = body.peekFirst() % width;
        switch(direction){
            case "U": rowHead--;
                break;
            case "D": rowHead++;
                break;
            case "L": colHead--;
                break;
            default: colHead++;
        }
        int head =  rowHead * width + colHead;
        
        //case 1: out of boundary or eating body
        set.remove(body.peekLast());
        if(rowHead < 0 || rowHead == height || colHead < 0 || colHead == width || set.contains(head)) return -1;
        
        // add head for case 2 and case3
        set.add(head);
        body.offerFirst(head);
        
        //case 2: eating food, keet tail, add head
        if(foodIndex<food.length && rowHead == food[foodIndex][0] && colHead == food[foodIndex][1]){
            set.add(body.peekLast());//keep the old tail
            foodIndex++;
            score++;
            return score;
        }
        
        //case3: normal more, remove tail, add head
        body.pollLast();
        return score;
    }
}

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