convert_binary_number_linked_list.rb

# Definition for singly-linked list.
# class ListNode
#     attr_accessor :val, :next
#     def initialize(val = 0, _next = nil)
#         @val = val
#         @next = _next
#     end
# end
# @param {ListNode} head
# @return {Integer}
def get_decimal_value(head)
    numbers = []
    current = head
    while current
       numbers << current.val 
       current = current.next
    end
    
    size = numbers.size 
    total = 0
    numbers.each do |n|
       break if size == 0
       total = total + (2 ** (size-1) * n)
       size -= 1
    end
    total
end

Refactored solution:

def get_decimal_value(head)
    numbers = []
    current = head
    while current
       numbers << current.val 
       current = current.next
    end
    
    size = numbers.size 
    total = 0
    numbers.each do |item|
      total = total + (2 ** (size-1) * item)
      size -= 1
    end
    total
end