[TASK] Day 2 part 2

day2-elixir/lib/day2.ex

@@ -5,26 +5,55 @@ defmodule Day2 do
   require Integer
 
   def start(_type, _args) do
-
     input_file = File.read("input/day2.txt")
-    IO.puts "Part 1: #{Day2.part1(elem(input_file, 1))}"
+    IO.puts("Part 1: #{Day2.part1(elem(input_file, 1))}")
+    IO.puts("Part 2: #{Day2.part2(elem(input_file, 1))}")
+
+    opts = [strategy: :one_for_one, name: A.Supervisor]
+    Supervisor.start_link([], opts)
   end
 
   def part1(input) do
+    eval(input, &Day2.is_invalid_id_pt1/1)
+  end
+
+  def part2(input) do
+    eval(input, &Day2.is_invalid_id_pt2/1)
+  end
+
+  def eval(input, id_checker) do
     for range <- String.split(input, ",") do
       [from, to] = String.split(range, "-") |> Enum.map(fn s -> String.to_integer(s) end)
-      eval_range(from, to)
-    end |> Enum.sum
+      eval_range(from, to, id_checker)
+    end
+    |> Enum.sum()
   end
 
-  def eval_range(from, to) do
-    Enum.filter(from..to, fn x -> is_valid_id(x) end) |> Enum.sum
+  def eval_range(from, to, id_checker) do
+    Enum.filter(from..to, fn x -> id_checker.(x) end) |> Enum.sum()
   end
 
-  def is_valid_id(id) do
+  def is_invalid_id_pt1(id) do
     digit_count = Enum.count(Integer.digits(id))
-    power = 10 ** (div(digit_count, 2))
+    power = 10 ** div(digit_count, 2)
     # IO.inspect {id, digit_count, power, div(id, power), rem(id, power)}
     Integer.is_even(digit_count) && div(id, power) == rem(id, power)
   end
+
+  def is_invalid_id_pt2(id) do
+    if id <= 10 do
+      false
+    else
+      id_digits = Integer.digits(id)
+      digit_count = Enum.count(id_digits)
+
+      res =
+        Enum.any?(1..div(digit_count, 2), fn pattern_size ->
+          sections = Enum.chunk_every(id_digits, pattern_size)
+          Enum.all?(Enum.drop(sections, 1), fn x -> x == Enum.at(sections, 0) end)
+        end)
+
+      res
+    end
+  end
 end