Day 22

1 files changed, 65 insertions, 0 deletions

diff --git a/src/day22.exs b/src/day22.exs
new file mode 100644
index 0000000..418631f
--- /dev/null
+++ b/src/day22.exs
@@ -0,0 +1,65 @@
+defmodule Day22 do
+  def part1(data, n \\ 2000) do
+    data
+    |> String.split("\n", trim: true)
+    |> Enum.map(&String.to_integer/1)
+    |> Enum.map(&(secret_numbers(&1, n)))
+    |> Enum.map(&hd/1)
+    |> Enum.sum()
+  end
+
+  defp secret_numbers(v, n) do
+    for _ <- 1..n, reduce: [v] do
+      v ->
+        [(v |> hd() |> change_value(6) |> change_value(-5) |> change_value(11)) | v]
+    end
+  end
+
+  defp change_value(v, shift) do
+    v
+    |> Bitwise.bsl(shift)
+    |> Bitwise.bxor(v)
+    |> Integer.mod(16777216)
+  end
+
+  def part2(data, n \\ 2000) do
+    data
+    |> String.split("\n", trim: true)
+    |> Enum.map(&String.to_integer/1)
+    |> Enum.map(&(secret_numbers(&1, n)))
+    |> Enum.map(&(sequences(&1, 10)))
+    |> Enum.reduce(%{}, fn s, acc ->
+      Map.merge(acc, s, fn _k, v1, v2 -> v1 + v2 end)
+    end)
+    |> Map.values()
+    |> Enum.max()
+  end
+
+  defp sequences(vs, m) do
+    vs
+    |> Enum.map(&Integer.mod(&1, m))
+    |> Enum.chunk_every(5, 1, :discard) # performance here could be improved
+    |> Enum.map(fn chunk -> {diffs(chunk), hd(chunk)} end)
+    |> Map.new()
+  end
+
+  defp diffs(vs) do
+    vs
+    |> Enum.chunk_every(2, 1, :discard)
+    |> Enum.map(fn [a, b] -> a - b end)
+    |> List.to_tuple()
+  end
+end
+
+data = IO.read(:stdio, :eof)
+
+{time1, ans1} = :timer.tc(fn -> Day22.part1(data) end)
+IO.puts("Time  : #{time1 / 1000000}")
+IO.puts("Answer: #{ans1}") # 19822877190
+
+{time2, ans2} = :timer.tc(fn -> Day22.part2(data) end)
+IO.puts("Time  : #{time2 / 1000000}")
+IO.puts("Answer: #{ans2}") # 2277
+
+
+