T pop()
{//出队
if (B.empty())
{//若B空，则队首元素应该在A的栈底
while (!A.empty())//将A中元素全部压入B
B.push(A.pop());
}
return B.pop();//出B栈
}
int max()
{
if (empty()) return 0;
if (head.empty())
return tail.max();
if (tail.empty())
return head.max();
else
return std::max(tail.max(),head.max());
}
void pop()
{
if (head.empty())
{
while (!tail.empty())
{
head.push(tail.top());
tail.pop();
}
}
head.pop();
}
bool empty()const { return A.empty() && B.empty(); }
bool empty ()
{
return head.empty() && tail.empty();
}