353. Design Snake Game

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)

Credits:
Special thanks to @elmirap for adding this problem and creating all test cases.

写一个贪吃蛇的程序，每吃到一个food，长度加一，撞墙或者咬到自己会死。这里用queue，和hashset记录目前所占的区域，queue主要负责更新区域，hashset主要负责查看会不会咬到自己。有一点注意的是有时下一步的位移是上一步的结尾，这时肯定是可行的，这时过早往hashset添加head是重复的，待会儿删除时，会把尾巴删掉，刚添加的头因为与尾巴相同，被删掉了，需要记得补回来。代码如下：

public class SnakeGame {    Queue<Integer> queue = new LinkedList<Integer>();    HashSet<Integer> hs = new HashSet<Integer>();    int[][] foods;    int foodIndex;    int width, height;    int currRow, currCol;    /** 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) {        queue.offer(0);        hs.add(0);        this.foods = food;        this.foodIndex = 0;        this.width = width;        this.height = height;        currRow = 0;        currCol = 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("U")) {            currRow --;        } else if (direction.equals("D")) {            currRow ++;        } else if (direction.equals("L")) {            currCol --;        } else if (direction.equals("R")) {            currCol ++;        }        int head = currRow * width + currCol;        /*System.out.print(direction);        System.out.print(head);        System.out.println(queue.peek());        System.out.println(hs);*/        if (head != queue.peek() && hs.contains(head)) {            return -1;        }        if (currRow >= 0 && currRow < height && currCol >= 0 && currCol < width) {            queue.offer(head);            hs.add(head);            if (foodIndex < foods.length && currRow == foods[foodIndex][0] && currCol == foods[foodIndex][1]) {                foodIndex ++;            } else {                int trail = queue.poll();                hs.remove(trail);                if (head == trail)                    hs.add(head);            }            return foodIndex;        }        return -1;    }}/** * Your SnakeGame object will be instantiated and called as such: * SnakeGame obj = new SnakeGame(width, height, food); * int param_1 = obj.move(direction); */