LeetCode *** 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 onlypush to back, peek/pop from front, size, andis 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).

Update (2015-06-11):
The class name of the Java function had been updated to MyStack instead of Stack.

分析：

利用queue扩展stack，用一个queue，然后用一个int数组来记录queue的值就可以了。

代码：

class Stack {    queue<int> myQ;    public:    // Push element x onto stack.    void push(int x) {        int size=myQ.size();        int *tmp=new int[size];                for(int i=0;i<size;++i){            tmp[i]=myQ.front();            myQ.pop();        }                myQ.push(x);                for(int i=0;i<size;++i)            myQ.push(tmp[i]);    }    // Removes the element on top of the stack.    void pop() {        myQ.pop();    }    // Get the top element.    int top() {        return myQ.front();    }    // Return whether the stack is empty.    bool empty() {        return myQ.empty();    }};