Complete day 5 part 2

Author: ctlevi

day5.exs

@@ -1,25 +1,64 @@
 defmodule Day5 do
+  # Part 2 functions
+  def how_many_nice_part_2(words) do
+    Enum.reduce(words, 0, fn (word, count) ->
+      count + (if naughty_or_nice_part_2(word) == :nice, do: 1, else: 0)
+    end)
+  end
+
+  def naughty_or_nice_part_2(word) do
+    if has_two_letters_repeating_twice?(word) && repeats_with_one_letter_between?(word), do: :nice, else: :naughty
+  end
+
+  def has_two_letters_repeating_twice?(word) do
+    prepared_word = remove_exactly_three_in_a_row(word)
+    all_pairs = Enum.chunk(prepared_word, 2) ++ Enum.chunk(tl(prepared_word), 2)
+    length(Enum.uniq(all_pairs)) < length(all_pairs)
+  end
+
+  defp remove_exactly_three_in_a_row([h | rest = [h2 | [h3 | [ h4  | _]]]], previous \\ '') do
+    if h == h2 && h == h3 && h != h4 && h != previous do
+      remove_exactly_three_in_a_row(rest, h)
+    else
+      [h | remove_exactly_three_in_a_row(rest, h)]
+    end
+  end
+  defp remove_exactly_three_in_a_row(rest = [h, h2, h3], previous), do: if h == h2 && h == h3 && h != previous, do: [h, h], else: rest
+  defp remove_exactly_three_in_a_row(rest, previous), do: rest
+
+  defp repeats_with_one_letter_between?(word) do
+    if length(word) < 3 do
+      false
+    else
+      Enum.zip(word, tl(word))
+      |> Enum.zip(word |> tl |> tl)
+      |> Enum.map(fn {{x, y}, z} -> [x, y, z] end)
+      |> Enum.any?(fn [first, _, last] -> first == last end)
+    end
+  end
+
+  # Part 1 functions
   def how_many_nice(words) do
     Enum.reduce(words, 0, fn (word, count) ->
       count + (if naughty_or_nice(word) == :nice, do: 1, else: 0)
     end)
   end
 
   defp naughty_or_nice(word) do
-    if has_three_vowels(word) && has_repeating_letter(word) && all_allowed(word), do: :nice, else: :naughty
+    if has_three_vowels?(word) && has_repeating_letter?(word) && all_allowed?(word), do: :nice, else: :naughty
   end
 
-  defp has_three_vowels(word) do
+  defp has_three_vowels?(word) do
     Enum.reduce([?a, ?e, ?i, ?o, ?u], 0, fn (vowel, count) ->
       count + length(Enum.filter(word, fn letter -> letter == vowel end))
     end) >= 3
   end
 
-  defp has_repeating_letter(word) do
+  defp has_repeating_letter?(word) do
     length(Enum.dedup(word)) < length(word)
   end
 
-  defp all_allowed(word) do
+  defp all_allowed?(word) do
     word_as_string = to_string(word)
     Enum.reduce(["ab", "cd", "pq", "xy"], true, fn (not_allowed, previous_check) ->
       previous_check && !String.contains?(word_as_string, not_allowed)
@@ -34,3 +73,4 @@ parsed_words = input
   |> Enum.map(&to_char_list/1)
 
 IO.inspect Day5.how_many_nice(parsed_words)
+IO.inspect Day5.how_many_nice_part_2(parsed_words)