剑指offer——用两个堆栈实现一个队列

class Solution
{
public:
void push(int node) {
stack1.push(node);
}

int pop() {
int a;
if(stack2.empty())
{
while(!stack1.empty()){
a=stack1.top();
stack2.push(a);
stack1.pop();//c++ stack::pop()无返回值
}
}
a=stack2.top();
stack2.pop();
return a;
}

private:
stack<int> stack1;
stack<int> stack2;
};