225. Implement Stack using Queues

题目：

Implement the following operations of a stack using queues.

• push(x) -- Push element x onto stack.
• pop() -- Removes the element on top of the stack.
• top() -- Get the top element.
• empty() -- Return whether the stack is empty.

Notes:

• You must use only standard operations of a queue -- which means only push to back, peek/pop from front, size, and is empty operations are valid.
• Depending on your language, queue may not be supported natively. You may simulate a queue by using a list or deque (double-ended queue), as long as you use only standard operations of a queue.
• You may assume that all operations are valid (for example, no pop or top operations will be called on an empty stack).

思路：

本题的采用dqueue的数据结构

代码：

class MyStack {public:    /** Initialize your data structure here. */    MyStack() {            }    deque<int> mystack;    /** Push element x onto stack. */    void push(int x) {        mystack.push_back(x) ;            }        /** Removes the element on top of the stack and returns that element. */    int pop() {        int temp = mystack.back();        mystack.pop_back();        return temp;                    }        /** Get the top element. */    int top() {        return mystack.back();            }        /** Returns whether the stack is empty. */    bool empty() {        return mystack.empty();            }};/** * Your MyStack object will be instantiated and called as such: * MyStack obj = new MyStack(); * obj.push(x); * int param_2 = obj.pop(); * int param_3 = obj.top(); * bool param_4 = obj.empty(); */