2024 Day 21

Author: zacklukem

2024/lib/day22.ex

@@ -0,0 +1,90 @@
+defmodule Day22a do
+  import Bitwise
+
+  def prune(sec) do
+    rem(sec, 16_777_216)
+  end
+
+  def mix(x, sec) do
+    bxor(sec, x)
+  end
+
+  def evolve(sec) do
+    sec = mix(sec * 64, sec) |> prune()
+    sec = mix(div(sec, 32), sec) |> prune()
+    sec = mix(sec * 2048, sec) |> prune()
+    sec
+  end
+
+  def run do
+    File.read!(".input.txt") |> run
+  end
+
+  def run(input) do
+    input
+    |> String.split("\n")
+    |> Enum.map(&String.to_integer/1)
+    |> Enum.map(fn sec ->
+      1..2000
+      |> Enum.reduce(sec, fn _, sec ->
+        evolve(sec)
+      end)
+    end)
+    |> Enum.sum()
+  end
+end
+
+defmodule Day22b do
+  import Bitwise
+
+  def prune(sec) do
+    rem(sec, 16_777_216)
+  end
+
+  def mix(x, sec) do
+    bxor(sec, x)
+  end
+
+  def evolve(sec) do
+    sec = mix(sec * 64, sec) |> prune()
+    sec = mix(div(sec, 32), sec) |> prune()
+    sec = mix(sec * 2048, sec) |> prune()
+    sec
+  end
+
+  def run do
+    File.read!(".input.txt") |> run
+  end
+
+  def run(input) do
+    maps =
+      input
+      |> String.split("\n")
+      |> Enum.map(&String.to_integer/1)
+      |> Enum.map(fn sec ->
+        {diffs, _} =
+          1..2000
+          |> Enum.map_reduce(sec, fn _, sec ->
+            secp = evolve(sec)
+            {{rem(secp, 10) - rem(sec, 10), secp}, secp}
+          end)
+
+        Enum.zip(0..3 |> Enum.map(&Enum.drop(diffs, &1)))
+        |> Enum.map(fn x ->
+          {
+            x |> Tuple.to_list() |> Enum.map(&elem(&1, 0)) |> List.to_tuple(),
+            rem(x |> elem(3) |> elem(1), 10)
+          }
+        end)
+        |> Enum.reverse()
+        |> Map.new()
+      end)
+
+    maps
+    |> Enum.reduce(fn a, b ->
+      Map.merge(a, b, fn _, a, b -> a + b end)
+    end)
+    |> Map.values()
+    |> Enum.max()
+  end
+end

2024/test/day22_test.exs

@@ -0,0 +1,16 @@
+defmodule Day22Test do
+  use ExUnit.Case
+
+  def example, do: "1
+10
+100
+2024"
+
+  test "Part 1 Example" do
+    assert Day22a.run(example()) == 37_327_623
+  end
+
+  # test "Part 2 Example" do
+  #   assert Day22b.run(example()) == 24
+  # end
+end