Leetcode_1279_红绿灯路口_多线程_1279. traffic light controlled intersection-优快云博客

本文链接：https://blog.youkuaiyun.com/HDUCheater/article/details/115046822

本文介绍了一种使用布尔变量和信号量实现交通灯控制的方法。通过一个`TrafficLight`类，可以确保不同道路上的车辆在交叉口正确通行。当车辆到达时，程序会检查当前灯的状态并决定是否改变灯的颜色。

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用一个布尔型变量保存目前红绿灯状态。
如果目前的车能通过红绿灯，就让他通过。
如果不能，改变灯的状态。

class TrafficLight {
    boolean isAGreen;    

    public TrafficLight() {
        isAGreen = true;
    }
    
    synchronized public void carArrived(
        int carId,           // ID of the car
        int roadId,          // ID of the road the car travels on. Can be 1 (road A) or 2 (road B)
        int direction,       // Direction of the car
        Runnable turnGreen,  // Use turnGreen.run() to turn light to green on current road
        Runnable crossCar    // Use crossCar.run() to make car cross the intersection 
    ) {
        if(roadId == 2 && isAGreen==true ||roadId == 1 && isAGreen == false)
        {
            turnGreen.run();
            isAGreen = !isAGreen;
        }
        crossCar.run();
    }
}

当然也可以用信号量的方法，相对速度肯定慢。

class TrafficLight {
    private Semaphore s;
    boolean isAGreen;
    public TrafficLight() {
        s = new Semaphore(1);
        isAGreen = true;
    }
    public void carArrived(
            int carId,           // ID of the car
            int roadId,          // ID of the road the car travels on. Can be 1 (road A) or 2 (road B)
            int direction,       // Direction of the car
            Runnable turnGreen,  // Use turnGreen.run() to turn light to green on current road
            Runnable crossCar    // Use crossCar.run() to make car cross the intersection 
    ) throws InterruptedException {
        s.acquire();
        if(roadId == 2 && isAGreen==true ||roadId == 1 && isAGreen == false)
        {
            turnGreen.run();
            isAGreen = !isAGreen;
        }
        crossCar.run();
        s.release();
    }
}