partition_list.rb

# Definition for singly-linked list. https://leetcode.com/problems/partition-list/submissions/
# class ListNode
#     attr_accessor :val, :next
#     def initialize(val = 0, _next = nil)
#         @val = val
#         @next = _next
#     end
# end
# @param {ListNode} head
# @param {Integer} x
# @return {ListNode}
def partition(head, x)
    list = ListNode.new
    first = list
    
    list2 = ListNode.new
    second = list2
    
    current = head
    
    while current
       if current.val < x
          first.next = ListNode.new(current.val)
          first = first.next
       else
           second.next = ListNode.new(current.val)
           second = second.next
       end
        current = current.next
    end
    
    current = list
    while current.next
        current = current.next
    end
    
    current.next = list2.next
    
    return list.next
end

Refactored code:

# 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
# @param {Integer} x
# @return {ListNode}
def partition(head, x)
    list = ListNode.new
    first = list
    
    list2 = ListNode.new
    second = list2
    
    current = head
    
    while current
       if current.val < x
          first.next = ListNode.new(current.val)
          first = first.next
       else
           second.next = ListNode.new(current.val)
           second = second.next
       end
        current = current.next
    end
    
    first.next = list2.next
    
    return list.next
end