leetcode 232. 用栈实现队列

class MyQueue {
public:
    /** Initialize your data structure here. */
    stack<int>in,out;
    
    void transferable()
    {
        while(!in.empty())
        {
            out.push(in.top());
            in.pop();
        }
    }

    MyQueue() 
    {
    }
    
    /** Push element x to the back of queue. */
    void push(int x) 
    {
        in.push(x);
    }
    
    /** Removes the element from in front of queue and returns that element. */
    int pop() 
    {
        if(out.empty())
        {
            transferable();
        }
        int x= out.top();
        out.pop();
        return x;
    }
    
    /** Get the front element. */
    int peek() 
    {
        if(out.empty())
        {
            transferable();
        }
        return out.top();
    }
    
    /** Returns whether the queue is empty. */
    bool empty() 
    {
        return in.empty()&&out.empty();        
    }
};