merge-two-sorted-list.ex

#pattern matching

# Definition for singly-linked list.
#
# defmodule ListNode do
#   @type t :: %__MODULE__{
#           val: integer,
#           next: ListNode.t() | nil
#         }
#   defstruct val: 0, next: nil
# end

defmodule Solution do
  @spec merge_two_lists(list1 :: ListNode.t | nil, list2 :: ListNode.t | nil) :: ListNode.t | nil

  def merge_two_lists(nil, second), do: second
  def merge_two_lists(first, nil), do: first
  def merge_two_lists(%{val: val1, next: next1} = first_list, %{val: val2, next: next2} = second_list) when val1 <= val2 do 
    %ListNode{val: val1, next: merge_two_lists(first_list.next, second_list)}                  
  end
      
  def merge_two_lists(%{val: val1, next: next1} = first_list, %{val: val2, next: next2} = second_list) do 
    %ListNode{val: val2, next: merge_two_lists(first_list, second_list.next)}                  
  end
end