这个程序的运行流程和5.8里面的那个倒计时有点相似。我们用3作为参数来调用一下这个阶乘函数试试。

The flow of execution for this program is similar to the flow of countdown in Section 5.8. If we call factorial with the value 3.

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只需将三种最常用的时间编入程序，以后就再不用设置倒计时间了。

Program the three most frequently used times and never set countdown times again.

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