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

    int pop()
    {
        if (empty())
        {
            return -1;
        }
        else
        {
            auto val = peek();
            out.pop();
            return val;
        }
    }

    int peek()
    {
        if (empty())
        {
            return -1;
        }
        else
        {
            if (out.empty())
            {
                while (!in.empty())
                {
                    auto val = in.top();
                    in.pop();
                    out.push(val);
                }
            }
            return out.top();
        }
    }

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

private:
    std::stack<int> in;
    std::stack<int> out;
};

/**
 * 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