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hcx2013
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Implement Stack using Queues

 
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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 backpeek/pop from frontsize, 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).
class MyStack {
	private LinkedList<Integer> queue = new LinkedList<>();
    // Push element x onto stack.
    public void push(int x) {
        queue.offer(x);
        int size = queue.size() - 1;
        while (size > 0) {
        	queue.offer(queue.poll());
        	size--;
        }
    }

    // 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();
    }
}

 

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