嘔嘔嘔
當 Pycon 志工還要寫這個真D累
所以我要偷懶一下 ;)

沒錯，直接延續昨天內容，但今天來複製貼上一下：用 stack 做 queue 吧！

class MyQueue {
     stack<int> input, output;
public:
    /** Initialize your data structure here. */
    MyQueue() {
        
    }
    
    /** Push element x to the back of queue. */
    void push(int x) {
         input.push(x);
    }
    
    /** Removes the element from in front of queue and returns that element. */
    int pop() {
        peek();
        return output.top();
    }
    
    /** Get the front element. */
    int peek() {
         if (output.empty())
            while (input.size())
                output.push(input.top()), input.pop();
        return output.top();
    }
    
    /** Returns whether the queue is empty. */
    bool empty() {
         return input.empty() && output.empty();
    }
};

這一題也是前兩天提到演算法聖經裡有的一題呢！

Show how to implement a stack using two queues. Analyze the running time of the stack operations.