用两个栈实现队列

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

    int pop() {
      int node;
        if(stack2.empty()){
            while(!stack1.empty()){
                node=stack1.top();
                stack1.pop();
                stack2.push(node);
            }           
        }
        node=stack2.top();
        stack2.pop(); 
        return node;
    }

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