create LinkedList class

linked_list.rb

#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
    end

    #push: given a data, add a new node in the end
    def push(data)
        if self.is_empty?
            @head = Node.new(data)
        else
            current_node = @head
            new_node = Node.new(data)
            while current_node.next != nil
                current_node = current_node.next 
            end
            current_node.next = new_node
        end
    end

    #unshift: add a new node in the front
    def unshift(data)
        if self.is_empty?
            @head = Node.new(data)
        else
            curr_head = Node.new(data)
            curr_head.next = @head 
            @head = curr_head
        end
    end

    #pop: remove the last node and return it
    def pop 
        if self.is_empty?
            return "Can't pop the element, this list is currently empty"
        else
            current_node = @head 
            while current_node.next.next != nil
                current_node = current_node.next 
            end
            last_node = current_node.next 
            current_node.next = nil 
        end
        last_node
    end


    #shift: remove the first node and return it
    def shift 
        if self.is_empty?
            return "This list is currently empty"
        else
            curr_head = @head
            new_head = @head.next 
            @head.next = nil 
            @head = new_head
        end
        curr_head
    end

    #size: return the length of linked list
    def size 
        if self.is_empty?
            count = 0 
        else
            count = 1 
            current_node = @head 
            while current_node.next != nil 
                current_node = current_node.next 
                count += 1
            end
        end
        count 
    end

    
    #pretty_print: print the current linked list as an array
    def pretty_print
        array = []
        current_node = @head 
        if self.is_empty?
            return array
        else 
            while current_node.next != nil
                array << current_node.data 
                current_node = current_node.next
            end
            array << current_node.data 
        end
        array
    end


    #clear: clear the whole linked list
    def clear 
        @head = nil 
    end
end