题解 | #用两个栈实现队列#

class Solution
{
public:
    void push(int node) {
        s1.push(node);
        return;
    }

    int pop() {
        int res;
        while (!s1.empty()) {
            s2.push(s1.top());
            s1.pop();
        }
        // s2的顶元素
	  	res = s2.top();
        s2.pop();
	  	// s2剩余的再pop到s1中
        while (!s2.empty()) {
            s1.push(s2.top());
            s2.pop();
        }
        return res;
    }

private:
    stack<int> s1;
    stack<int> s2;
};