2024 Day 25

Author: zacklukem

2024/lib/day25.ex

@@ -0,0 +1,43 @@
+defmodule Day25a do
+  def run do
+    File.read!(".input.txt") |> run
+  end
+
+  def fits?(a, b) do
+    Enum.zip(a, b)
+    |> Enum.all?(fn {a, b} -> a + b <= 5 end)
+  end
+
+  def run(input) do
+    {locks, keys} =
+      input
+      |> String.split("\n\n")
+      |> Enum.reduce({[], []}, fn pattern, {locks, keys} ->
+        pattern =
+          pattern
+          |> String.split("\n")
+          |> Enum.map(&(&1 |> String.to_charlist()))
+
+        heights =
+          pattern
+          |> tl()
+          |> Enum.take(5)
+          |> Enum.reduce([0, 0, 0, 0, 0], fn line, heights ->
+            Enum.zip(heights, line)
+            |> Enum.map(fn {h, cell} -> h + if cell == ?#, do: 1, else: 0 end)
+          end)
+
+        if hd(pattern) == ~c"#####" do
+          {[heights | locks], keys}
+        else
+          {locks, [heights | keys]}
+        end
+      end)
+
+    locks
+    |> Enum.map(fn lock ->
+      keys |> Enum.count(fn key -> fits?(lock, key) end)
+    end)
+    |> Enum.sum()
+  end
+end

2024/test/day25_test.exs

@@ -0,0 +1,13 @@
+defmodule Day25Test do
+  use ExUnit.Case
+
+  def example, do: ""
+
+  test "Part 1 Example" do
+    assert Day25a.run(example()) == :todo
+  end
+
+#   test "Part 2 Example" do
+#     assert Day25b.run(example()) == :todo
+#   end
+end