Q3.2 带有最小值或最大值的栈

How would you design a stack which, in addition to push and pop, also has a function min which returns the minimum element? Push, pop and min should all operate in O(1) time.

template<class T>
class StackWithMin
{
public:
    stack()
    {
        stackTop = -1;
        minStackItemIndex = -1;
    }
    void Push(T x)
    {    stackTop++;
        if(stackTop>MAXN)
           //超出栈的最大存储量；
        else 
        {
            stackItem[stackTop] = x;
            if(x<Min())
            {
                NextMinItem[stackTop] = minStackItemIndex;
                minStackItemIndex = stackTop;
            }
            else
                NextMinItem[stackTop] = -1;
        }
    }
    void Pop()
    {
        if(stackTop<0)
            ThrowException();
        else
        {
            if(stackTop == minStackItemIndex)
                minStackItemIndex = NextMinItem[stackTop];
            stackTop--;
        }
    }
    T Top()
    {
        return stackItem[stackTop];
    }
    T Min()
    {
        if(minStackItemIndex>=0)
            return stackItem[minStackItemIndex];
        else
            return INT_MAX;
    }
    
private:
    T stackItem[MAXN];
    int stackTop;
    int NextMinItem[MAXN];
    int minStackItemIndex;

};