实现5部电梯，20层楼的电梯调度程序。存在的问题：

由于在写调度算法时， 用的是顺序遍历这5个线程， 导致0号线程总是最有可能被调用， 4号线程总是最有可能空闲， 这是对资源的不太高效的利用， 有待改进。-Achieve 5 lifts, 20 floors of the elevator scheduler. Problems: Since writing the scheduling algorithm, using a sequence through these five threads, resulting in 0 thread is always most likely to be called, 4 thread is always the most likely to idle, which is not of resources efficient use of room for improvement.