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| 1 | +const { Queue } = require('../../src/index'); |
| 2 | + |
| 3 | +// tag::description[] |
| 4 | +/** |
| 5 | + * The snake game stars with a snake of length 1 at postion 0,0. |
| 6 | + * Only one food position is shown at a time. Once it's eaten the next one shows up. |
| 7 | + * The snake can move in four directions up, down, left and right. |
| 8 | + * If the snake go out of the boundaries (width x height) the game is over. |
| 9 | + * If the snake hit itself the game is over. |
| 10 | + * When the game is over, the `move` method returns -1 otherwise, return the current score. |
| 11 | + * |
| 12 | + * @example |
| 13 | + * const snakeGame = new SnakeGame(3, 2, [[1, 2], [0, 1]]); |
| 14 | + * snakeGame.move('R'); // 0 |
| 15 | + * snakeGame.move('D'); // 0 |
| 16 | + * snakeGame.move('R'); // 0 |
| 17 | + * snakeGame.move('U'); // 1 (ate the food1) |
| 18 | + * snakeGame.move('L'); // 2 (ate the food2) |
| 19 | + * snakeGame.move('U'); // -1 (hit the upper wall) |
| 20 | + */ |
| 21 | +class SnakeGame { |
| 22 | +// end::description[] |
| 23 | +// tag::solution[] |
| 24 | + |
| 25 | + // end::solution[] |
| 26 | + // tag::description[] |
| 27 | + /** |
| 28 | + * Initialize game with grid's dimension and food order. |
| 29 | + * @param {number} width - The screen width (grid's columns) |
| 30 | + * @param {number} height - Screen height (grid's rows) |
| 31 | + * @param {number[]} food - Food locations. |
| 32 | + */ |
| 33 | + constructor(width, height, food) { |
| 34 | + // end::description[] |
| 35 | + // tag::solution[] |
| 36 | + this.width = width; |
| 37 | + this.height = height; |
| 38 | + this.food = new Queue(food); |
| 39 | + this.snake = new Queue([[0, 0]]); |
| 40 | + this.tail = new Set([[0, 0]]); |
| 41 | + this.dirs = { |
| 42 | + U: [-1, 0], D: [1, 0], R: [0, 1], L: [0, -1], |
| 43 | + }; |
| 44 | + // end::solution[] |
| 45 | + // tag::description[] |
| 46 | + } |
| 47 | + // end::description[] |
| 48 | + |
| 49 | + // tag::description[] |
| 50 | + /** |
| 51 | + * Move snake 1 position into the given direction. |
| 52 | + * It returns the score or game over (-1) if the snake go out of bound or hit itself. |
| 53 | + * @param {string} direction - 'U' = Up, 'L' = Left, 'R' = Right, 'D' = Down. |
| 54 | + * @returns {number} - The current score (snake.length - 1). |
| 55 | + */ |
| 56 | + move(direction) { |
| 57 | + // end::description[] |
| 58 | + // tag::solution[] |
| 59 | + let [r, c] = this.snake.back(); // head of the snake |
| 60 | + [r, c] = [r + this.dirs[direction][0], c + this.dirs[direction][1]]; |
| 61 | + |
| 62 | + // check wall collision |
| 63 | + if (r < 0 || c < 0 || r >= this.height || c >= this.width) return -1; |
| 64 | + |
| 65 | + const [fr, fc] = this.food.front() || []; // peek |
| 66 | + if (r === fr && c === fc) { |
| 67 | + this.food.dequeue(); // remove eaten food. |
| 68 | + } else { |
| 69 | + this.snake.dequeue(); // remove snake's if not food was eaten |
| 70 | + this.tail.delete(this.tail.keys().next().value); |
| 71 | + } |
| 72 | + |
| 73 | + // check collision with snake's tail |
| 74 | + if (this.tail.has(`${r},${c}`)) return -1; // O(1) |
| 75 | + |
| 76 | + this.snake.enqueue([r, c]); // add new position |
| 77 | + this.tail.add(`${r},${c}`); |
| 78 | + |
| 79 | + return this.snake.size - 1; // return score (length of the snake - 1) |
| 80 | + // end::solution[] |
| 81 | + // tag::description[] |
| 82 | + } |
| 83 | +} |
| 84 | +// end::description[] |
| 85 | + |
| 86 | +module.exports = { SnakeGame }; |
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