Day 4 part 2 complete

Author: patrickdavey

2019/4/instructions.md

@@ -24,10 +24,33 @@ Other than the range rule, the following are true:
 *How many different passwords* within the range given in your puzzle
 input meet these criteria?
 
-Your puzzle input is `123257-647015`{.puzzle-input}.
+Your puzzle answer was `2220`.
+
+The first half of this puzzle is complete! It provides one gold star: \*
+
+--- Part Two --- {#part2}
+----------------
+
+An Elf just remembered one more important detail: the two adjacent
+matching digits *are not part of a larger group of matching digits*.
+
+Given this additional criterion, but still ignoring the range rule, the
+following are now true:
+
+-   `112233` meets these criteria because the digits never decrease and
+    all repeated digits are exactly two digits long.
+-   `123444` no longer meets the criteria (the repeated `44` is part of
+    a larger group of `444`).
+-   `111122` meets the criteria (even though `1` is repeated more than
+    twice, it still contains a double `22`).
+
+*How many different passwords* within the range given in your puzzle
+input meet all of the criteria?
+
+Your puzzle input is still `123257-647015`{.puzzle-input}.
 
 Answer:
 
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2019/4/lib/aoc/password_validator.ex

@@ -1,11 +1,21 @@
 # lib/aoc/password_validator.ex
 defmodule AOC.PasswordValidator do
-  def check(range, number) do
+  def check(number) do
     Regex.match?(~r/(\d)\1/, to_string(number)) &&
     only_increasing(String.graphemes(to_string(number)))
   end
 
+  def check2(number) do
+    only_increasing(String.graphemes(to_string(number))) && check_duplicates(number)
+  end
+
   defp only_increasing(chars) do
     chars == Enum.sort(chars)
   end
+
+  defp check_duplicates(number) do
+    lengths = Regex.scan(~r/(\d)\1+/, to_string(number)) |> Enum.map(&(Enum.at(&1 || [0], 0))) |> Enum.map(&(String.length/1))
+
+    lengths != [] && Enum.any?(lengths, &(&1 == 2))
+  end
 end

2019/4/lib/aoc/runner.ex

@@ -1,13 +1,16 @@
 defmodule AOC.Runner do
   alias AOC.PasswordValidator
+
   def part_1 do
     range
-    |> Enum.filter(&(PasswordValidator.check(range, &1)))
+    |> Enum.filter(&(PasswordValidator.check/1))
     |> length
   end
 
   def part_2 do
-    "part 2"
+    range
+    |> Enum.filter(&(PasswordValidator.check2/1))
+    |> length
   end
 
   defp range do

2019/4/test/aoc/password_validator_test.exs

@@ -3,8 +3,8 @@ defmodule AOCPasswordValidatorTest do
   alias AOC.PasswordValidator
 
   test "sample tests work" do
-    assert(PasswordValidator.check((0..999999), 111111) == true)
-    assert(PasswordValidator.check((0..999999), 123789) == false)
-    assert(PasswordValidator.check((0..999999), 223450) == false)
+    assert(PasswordValidator.check(111111) == true)
+    assert(PasswordValidator.check(123789) == false)
+    assert(PasswordValidator.check(223450) == false)
   end
 end