题解 | 用两个栈实现队列，思路是先把堆栈1全都倒出去，在堆栈2的顶部就是要输出的，去掉之后再倒回来

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

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

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