如果我们有两个相同类型的栈，我们为他们各自开辟了数组空间，极有可能第一个栈已经满了，再进栈就溢出了，而另一个栈还有很多存储空间空闲。这时，我们完全可以用一个数组两存储两个栈。(f we have two identical types of stack, we have opened up the array space for them. It is very likely that the first stack is full, then the stack will overflow,