232. 用栈实现队列

232. 用栈实现队列

使用两个栈，一个作为输入栈，一个作为输出栈

class MyQueue {
public:
    stack<int> in;
    stack<int> out;
    MyQueue() {
    }
    void push(int x) {
        in.push(x);
    }
    int pop() {
        if(out.empty())
        {
            while(!in.empty())
            {
                out.push(in.top());
                in.pop();
            }
        }
        int res = out.top();
        out.pop();
        return res;
    }
    int peek() {
        int res = this->pop();
        out.push(res);
        return res;
    }
    bool empty() {
        return in.empty()&&out.empty();
    }
};