232.用栈实现队列.cpp

/*
 * @lc app=leetcode.cn id=232 lang=cpp
 *
 * [232] 用栈实现队列
 */

// @lc code=start
class MyQueue
{
private:
    std::stack<int> in;
    std::stack<int> out;

public:
    MyQueue()
    {
    }

    void push(int x)
    {
        in.push(x);
    }

    int pop()
    {
        auto res = peek();
        out.pop();
        return res;
    }

    int peek()
    {
        if (out.size() <= 0)
        {
            while (in.size() > 0)
            {
                out.push(in.top());
                in.pop();
            }
        }
        return out.top();
    }

    bool empty()
    {
        return in.size() == 0 && out.size() == 0;
    }
};

/**
 * Your MyQueue object will be instantiated and called as such:
 * MyQueue* obj = new MyQueue();
 * obj->push(x);
 * int param_2 = obj->pop();
 * int param_3 = obj->peek();
 * bool param_4 = obj->empty();
 */
// @lc code=end