Microbit 游戏编程: 贪心算法也无法让贪吃蛇永生

function initSnake(arr: Array<number>) {
    let result = [];
    for (let i = 0; i + 1 < arr.length; i += 2) {
        result.push(game.createSprite(arr[i], arr[i + 1]));
    }
    return result;
};

let direction = 1; // initial direction is down
let dxOffset = [[1, 0], [0, 1], [-1, 0], [0, -1]];
let snake = initSnake([px, py, px + 1, py]);
//当蛇长到10像素时, 它停止增长
//避免填充LED
const maxLength = 10;

// 检查(x, y)是否为蛇体的坐标之一. 
function isOnSnake(x: number, y: number): boolean {
    for (let body of snake) {
        if (body.x() == x && body.y() == y) {
            return true;
        }
    }
    return false;
}
 
function validPixelCoordinate(nx: number, ny: number): boolean {
    return (nx >= 0 && nx <= 4 && 
            ny >= 0 && ny <= 4) && (!isOnSnake(nx, ny));
}

function placeNextApple() {
    let x, y;
    do {
        x = Math.randomRange(0, 4);
        y = Math.randomRange(0, 4);
    } while (isOnSnake(x, y));
    apple.goTo(x, y);
    apple.setBrightness(100);
}

function resetGame() {
    game.setScore(0);
    score = 0;
    direction = 0;
    px = 0;
    py = 0;
    // 释放蛇的身体和占用的内存
    for (let s of snake) {
        s.delete();
    }
    snake = initSnake([px, py, px + 1, py]);
    placeNextApple();
    game.resume();
}

function moveForward() {
    let dx = dxOffset[direction];
    px += dx[0];
    py += dx[1];
    if (!validPixelCoordinate(px, py)) {
        gameOver();
    }
    snake.unshift(game.createSprite(px, py));
    let last = snake.pop();
    last.delete();
}

basic.forever(function () {
    if (game.isGameOver()) {
        return;
    }
    let delay = Math.max(100, 1000 - score * 50);
    basic.pause(delay);
    //letComputerPlay();
    moveForward();
    if (snake[0].isTouching(apple)) { // 吃到了苹果
        // 在大于 maxLength 后就不长了
        if (snake.length < maxLength) {
            // 复制一个尾巴
            snake.push(snake[snake.length - 1]);
        }
        score++;
        placeNextApple();
    }
})