Leetcode 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).

 

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

 

class Stack

    # Initialize your data structure here.

    def initialize

        @q = Array.new

    end



    # @param {Integer} x

    # @return {void}

    def push(x)

        @q << x

    end



    # @return {void}

    def pop

       (@q.length-1).times {@q << @q.shift}

       @q.shift

    end



    # @return {Integer}

    def top

        (@q.length-1).times {@q << @q.shift}

        t = @q.shift

        @q << t

        t

    end



    # @return {Boolean}

    def empty

        @q.empty?

    end

end