1 files changed, 80 insertions, 0 deletions
diff --git a/src/day05.exs b/src/day05.exs
new file mode 100644
index 0000000..e950b06
--- /dev/null
+++ b/src/day05.exs
@@ -0,0 +1,80 @@
+defmodule Day05 do
+  def parse_integer_list(list, split) do
+    list
+    |> String.split(split, trim: true)
+    |> Enum.map(&String.to_integer/1)
+  end
+
+  def parse_data(data) do
+    [rules, jobs] = data
+    |> String.split("\n\n", trim: true)
+
+    rules = rules
+    |> String.split("\n", trim: true)
+    |> Enum.map(&parse_integer_list(&1, "|"))
+    |> Enum.group_by(&hd/1, &hd(tl(&1)))
+    |> Enum.into(%{}, fn {k, v} -> {k, MapSet.new(v)} end)
+
+    jobs = jobs
+    |> String.split("\n", trim: true)
+    |> Enum.map(&parse_integer_list(&1, ","))
+
+    {rules, jobs}
+  end
+
+  def part1({rules, jobs}) do
+    jobs
+    |> Enum.filter(&job_okay?(&1, rules))
+    |> Enum.map(&middle_page/1)
+    |> Enum.sum()
+  end
+
+  def job_okay?(job, rules) do
+    case job do
+      [] ->
+        true
+      [page | rest] ->
+        page_okay?(page, rest, rules) and
+          job_okay?(rest, rules)
+    end
+  end
+
+  def page_okay?(page, rest, rules) do
+    rest
+    |> Enum.all?(&Map.get(rules, &1, %MapSet{}) |> MapSet.member?(page) == false)
+  end
+
+  def middle_page(job) do
+    job |> Enum.at(job |> length() |> div(2))
+  end
+
+  def part2({rules, jobs}) do
+    jobs
+    |> Enum.reject(&job_okay?(&1, rules))
+    |> Enum.map(&fix_job(&1, rules))
+    |> Enum.map(&middle_page/1)
+    |> Enum.sum()
+  end
+
+  def fix_job(job, rules, acc \\ []) do
+    case job do
+      [] ->
+        Enum.reverse(acc)
+      job ->
+        {l, r} = Enum.split_with(job, &page_okay?(&1, job, rules) == false)
+        [next, rest] = [hd(r), l ++ tl(r)]
+        fix_job(rest, rules, [next | acc])
+    end
+  end
+end
+
+data = IO.read(:stdio, :eof) |> Day05.parse_data()
+
+{time1 , ans1} = :timer.tc(fn -> Day05.part1(data) end)
+IO.puts("Time  : #{time1 / 1000000}")
+IO.puts("Answer: #{ans1}")
+
+{time2 , ans2} = :timer.tc(fn -> Day05.part2(data) end)
+IO.puts("Time  : #{time2 / 1000000}")
+IO.puts("Answer: #{ans2}")
+