1117. H2O 生成

class H2O {
    private Semaphore h;
    private Semaphore o;

    public H2O() {
        h = new Semaphore(2);
        o = new Semaphore(0);
    }

    public void hydrogen(Runnable releaseHydrogen) throws InterruptedException {
        h.acquire();

        // releaseHydrogen.run() outputs "H". Do not change or remove this line.
        releaseHydrogen.run();
        o.release();
    }

    public void oxygen(Runnable releaseOxygen) throws InterruptedException {
        o.acquire(2);

        // releaseOxygen.run() outputs "O". Do not change or remove this line.
        releaseOxygen.run();
        h.release(2);
    }
}