(leetcode)Implement Stack using Queues

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).

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

Credits:
Special thanks to @jianchao.li.fighter for adding this problem and all test cases.

用一个队列就可实现，看了很多例子觉得discuss里面有个朋友写的很简练，就用了他的丝路，和她基本一致

 class Stack {
 public:
     // Push element x onto stack..
     queue<int> a;
     void push(int x) {
         a.push(x);
     }

     // Removes the element on top of the stack.
     void pop() {
         size_t i = ;
         size_t size = a.size();
         for(i = ; i < size-; ++i)
         {
             a.push(a.front());
             a.pop();
         }
         a.pop();
     }

     // Get the top element.
     int top() {
         return a.back();
     }

     // Return whether the stack is empty.
     bool empty() {
         return a.empty();
     }
 };