From 67ef614680b0d65c593ddde036b293da46f6c195 Mon Sep 17 00:00:00 2001
From: Adam Millerchip <adam@millerchip.net>
Date: Mon, 4 Sep 2023 00:11:03 +0900
Subject: [PATCH] Add 2015 Day 5

---
 2015/day5.exs | 86 +++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 86 insertions(+)
 create mode 100644 2015/day5.exs

diff --git a/2015/day5.exs b/2015/day5.exs
new file mode 100644
index 0000000..ec3b17a
--- /dev/null
+++ b/2015/day5.exs
@@ -0,0 +1,86 @@
+defmodule Day5 do
+  def part1(input) do
+    Enum.count(input, &nice?/1)
+  end
+
+  def nice?(str) do
+    at_least_three_vowels(str) and
+      twice_in_a_row(str) and
+      not String.contains?(str, ["ab", "cd", "pq", "xy"])
+  end
+
+  def at_least_three_vowels(str) do
+    str
+    |> String.graphemes()
+    |> Enum.frequencies()
+    |> Map.take(["a", "e", "i", "o", "u"])
+    |> Map.values()
+    |> Enum.sum()
+    |> Kernel.>=(3)
+  end
+
+  def twice_in_a_row(<<x, x, _::binary>>), do: true
+  def twice_in_a_row(<<_x, rest::binary>>), do: twice_in_a_row(rest)
+  def twice_in_a_row(<<>>), do: false
+
+  def part2(input) do
+   Enum.count(input, &nice2?/1)
+  end
+
+  def nice2?(str) do
+    pairs = pairs(str)
+    uniq = MapSet.new(pairs)
+    length(pairs) > MapSet.size(uniq) and sandwich(str)
+  end
+
+  def pairs(str, prev \\ nil)
+  def pairs(<<x, x, rest::binary>>, <<x, x>>), do: pairs(<<x, rest::binary>>)
+  def pairs(<<x, y, rest::binary>>, _prev), do: [<<x, y>> | pairs(<<y, rest::binary>>, <<x, y>>)]
+  def pairs(<<_>>, _prev), do: []
+
+  def sandwich(<<x, y, x, _rest::binary>>), do: true
+  def sandwich(<<_x, y, z, rest::binary>>), do: sandwich(<<y, z, rest::binary>>)
+  def sandwich(_), do: false
+
+  def input do
+    with [input_filename] <- System.argv(),
+         {:ok, input} <- File.read(input_filename) do
+      input
+      |> String.split("\n", trim: true)
+    else
+      _ -> :error
+    end
+  end
+
+  #######################
+  # HERE BE BOILERPLATE #
+  #######################
+
+  def run do
+    case input() do
+      :error -> print_usage()
+      input -> run_parts_with_timer(input)
+    end
+  end
+
+  defp run_parts_with_timer(input) do
+    run_with_timer(1, fn -> part1(input) end)
+    run_with_timer(2, fn -> part2(input) end)
+  end
+
+  defp run_with_timer(part, fun) do
+    {time, result} = :timer.tc(fun)
+    IO.puts("Part #{part} (completed in #{format_time(time)}):\n")
+    IO.puts("#{result}\n")
+  end
+
+  defp format_time(μsec) when μsec < 1_000, do: "#{μsec}μs"
+  defp format_time(μsec) when μsec < 1_000_000, do: "#{μsec / 1000}ms"
+  defp format_time(μsec), do: "#{μsec / 1_000_000}s"
+
+  defp print_usage do
+    IO.puts("Usage: elixir day5.exs input_filename")
+  end
+end
+
+Day5.run()