5、利用两个栈实现队列，完成push和pop操作

class Solution
{
public:
    void push(int node) {
        stack1.push(node);
    }
    int pop() {
        if(stack2.empty())
        {
            while(!stack1.empty())
            {
                int num = stack1.top();
                stack2.push(num);
                stack1.pop();
            }
        }
        int res = stack2.top();
        stack2.pop();
        return res;
            
    }

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