题解 | #用两个栈实现队列#

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

    int pop() {
        if(stack2.empty())
        {
            while(!stack1.empty())
            {
                int temp = stack1.top();
                stack2.push(temp);
                stack1.pop();
            }
        }
        int res = 0;
        res = stack2.top();
        stack2.pop();
        return res;
    }

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

另一种写法：

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

    int pop() {
        //将第一个栈中内容弹出放入第二个栈中
        while(!stack1.empty())
        {
            stack2.push(stack1.top());
            stack1.pop();
        }
        //第二个栈栈顶就是最先进来的元素，即队首
        int res = stack2.top();
        stack2.pop();
        //再将第二个栈的元素放回第一个栈
        while(!stack2.empty())
        {
            stack1.push(stack2.top());
            stack2.pop();
        }
        return res;
    }

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