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class Node
    
    attr_accessor :data, :next

    def initialize(data, next_node = nil)
        @data = data
        @next = next_node
    end
end

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#linked list is composed nodes, each node has a data, than it points to the next node
class LinkedList 

    #is_empty?: return true if the linked list is empty
    def is_empty?
        if @head == nil
            return true 
        else
            return false
        end

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class TreeNode 
    attr_accessor :value, :left, :right

    def initialize(value)
        @value = value
        @left = nil
        @right = nil
    end
end