225. 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).

Only push is O(n), others are O(1). Using one queue.

class MyStack 
{
    Queue<Integer> queue;
    
    public MyStack()
    {
        this.queue=new LinkedList<Integer>();
    }
    
    // Push element x onto stack.
    public void push(int x) 
    {
       queue.add(x);
       for(int i=0;i<queue.size()-1;i++)
       {
           queue.add(queue.poll());
       }
    }

    // Removes the element on top of the stack.
    public void pop() 
    {
        queue.poll();
    }

    // Get the top element.
    public int top() 
    {
        return queue.peek();
    }

    // Return whether the stack is empty.
    public boolean empty() 
    {
        return queue.isEmpty();
    }
}