LeetCode - Remove nth node form end of list

remove_nth_node_from_end_of_list.rb

# Definition for singly-linked list.
# class ListNode
#     attr_accessor :val, :next
#     def initialize(val)
#         @val = val
#         @next = nil
#     end
# end

# @param {ListNode} head
# @param {Integer} n
# @return {ListNode}
def remove_nth_from_end(head, n)
    node_length = linkedlist_length(head)
    counter = node_length
    current_node = head
    previous_node = nil
    
    loop do
        if counter == n
            delete_nth_node(previous_node, current_node)
            break
        end
        
        if !current_node.next.nil?
            previous_node = current_node
            current_node = current_node.next
        end
        
        counter -= 1
    end
    
    head
end

def delete_nth_node(previous_node, current_node)
    if !current_node.next.nil?
        current_node.val = current_node.next.val
        current_node.next = current_node.next.next
    else
        current_node.val = nil
        current_node.next = nil
        
        previous_node.next = nil if !previous_node.nil?
    end
end

def linkedlist_length(head, length = 0)
    return length if head.nil?
    
    length += 1
    linkedlist_length(head.next, length)
end