[LeetCode] Design Snake Game 設計貪吃蛇游戲

 

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.

 

感覺最近LeetCode經常出一些design類的題目啊，難道算法類的題目都出完了嗎，這道題讓我們設計一個貪吃蛇的游戲，這是個簡化版的，但是游戲規則還是保持不變，蛇可以往上下左右四個方向走，吃到食物就會變長1個，如果碰到牆壁或者自己的軀體，游戲就會結束。我們需要一個一維數組來保存蛇身的位置，由於蛇移動的過程的蛇頭向前走一步，蛇尾也跟着往前，中間的軀體還在原來的位置，所以移動的結果就是，蛇頭變到新位置，去掉蛇尾的位置即可。需要注意的是去掉蛇尾的位置是在檢測和蛇身的碰撞之前還是之后，如果是之后則無法通過這個test case：[[3,3,[[2,0],[0,0]]],["D"],["D"],["U"]]，如果是之前就沒有問題了，檢測蛇頭和蛇身是否碰撞使用的是count(snake.begin(), snake.end(), head)，總體來說不算一道難題，參見代碼如下：

 

class SnakeGame {
public:
    /** 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]. */
    SnakeGame(int width, int height, vector<pair<int, int>> food) {
        this->width = width;
        this->height = height;
        this->food = food;
        score = 0;
        snake.push_back({0, 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. */
    int move(string direction) {
        auto head = snake.front(), tail = snake.back();
        snake.pop_back();
        if (direction == "U") --head.first;
        else if (direction == "L") --head.second;
        else if (direction == "R") ++head.second;
        else if (direction == "D") ++head.first;
        if (count(snake.begin(), snake.end(), head) || head.first < 0 || head.first >= height || head.second < 0 || head.second >= width) {
            return -1;
        }
        snake.insert(snake.begin(), head);
        if (!food.empty() && head == food.front()) {
            food.erase(food.begin());
            snake.push_back(tail);
            ++score;
        }
        return score;
    }

private:
    int width, height, score;
    vector<pair<int, int>> food, snake;
}; 

 

參考資料:

https://leetcode.com/problems/design-snake-game/

https://leetcode.com/discuss/106235/c-solution-seems-test-case-didnt-consider-food-on-body

 

LeetCode All in One 題目講解匯總(持續更新中...)