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.

 class Stack {
 private:
     queue <int> q_1;
     queue <int> q_2;
 public:
     // Push element x onto stack.
     void push(int x) {
         if(q_1.empty())
           q_1.push(x);
         else
         {
             while(!q_1.empty())
             {
                 q_2.push(q_1.front());
                 q_1.pop();
             }
             q_1.push(x);
             while(!q_2.empty())
             {
                 q_1.push(q_2.front());
                 q_2.pop();
             }
         }
     }
 
     // Removes the element on top of the stack.
     void pop() {
         q_1.pop();
     }
 
     // Get the top element.
     int top() {
         return q_1.front();
     }
 
     // Return whether the stack is empty.
     bool empty() {
         return q_1.empty();
     }
 };