1 files changed, 95 insertions, 0 deletions
diff --git a/2015/day15.exs b/2015/day15.exs
new file mode 100644
index 0000000..8f93a1b
--- /dev/null
+++ b/2015/day15.exs
@@ -0,0 +1,95 @@
+ingredients =
+  File.stream!("inputs/day15.txt")
+  |> Enum.filter(fn line -> String.trim(line) != "" end)
+  |> Enum.map(fn line ->
+    Regex.run(
+      ~r/\w+: capacity ([+-]?\d+), durability ([+-]?\d+), flavor ([+-]?\d+), texture ([+-]?\d+), calories ([+-]?\d+)/,
+      line
+    )
+    |> Stream.drop(1)
+    |> Stream.map(&Integer.parse/1)
+    |> Enum.map(fn {i, _} -> i end)
+  end)
+
+ingredientsWithoutCalories =
+  Enum.map(ingredients, fn line ->
+    {_calories, withoutCalories} = List.pop_at(line, -1)
+    withoutCalories
+  end)
+
+ingredientsWithCalories =
+  Enum.map(ingredients, fn line ->
+    List.pop_at(line, -1)
+  end)
+
+defmodule RecipeFinder do
+  def findTastiestRecipe([lastIngredient], remainingSpoons, currentMixture) do
+    Enum.zip(lastIngredient, currentMixture)
+    |> Enum.map(fn {next, current} -> next * remainingSpoons + current end)
+    |> Enum.map(&max(&1, 0))
+    |> Enum.product()
+  end
+
+  def findTastiestRecipe([nextIngredient | remainingIngredients], remainingSpoons, currentMixture) do
+    Enum.map(0..remainingSpoons, fn nextSpoons ->
+      findTastiestRecipe(
+        remainingIngredients,
+        remainingSpoons - nextSpoons,
+        Enum.zip(nextIngredient, currentMixture)
+        |> Enum.map(fn {next, current} -> next * nextSpoons + current end)
+      )
+    end)
+    |> Enum.max()
+  end
+
+  def findTastiestRecipeWithExactCalories(
+        [{lastIngredientCalories, _}],
+        remainingSpoons,
+        remainingCalories,
+        _
+      )
+      when lastIngredientCalories * remainingSpoons != remainingCalories do
+    nil
+  end
+
+  def findTastiestRecipeWithExactCalories(
+        [{_, lastIngredient}],
+        remainingSpoons,
+        _,
+        currentMixture
+      ) do
+    Enum.zip(lastIngredient, currentMixture)
+    |> Enum.map(fn {next, current} -> next * remainingSpoons + current end)
+    |> Enum.map(&max(&1, 0))
+    |> Enum.product()
+  end
+
+  def findTastiestRecipeWithExactCalories(
+        [{nextIngredientCalories, nextIngredient} | remainingIngredients],
+        remainingSpoons,
+        remainingCalories,
+        currentMixture
+      ) do
+    maxSpoons = min(remainingSpoons, div(remainingCalories, nextIngredientCalories))
+
+    Enum.map(0..maxSpoons, fn nextSpoons ->
+      findTastiestRecipeWithExactCalories(
+        remainingIngredients,
+        remainingSpoons - nextSpoons,
+        remainingCalories - nextIngredientCalories * nextSpoons,
+        Enum.zip(nextIngredient, currentMixture)
+        |> Enum.map(fn {next, current} -> next * nextSpoons + current end)
+      )
+    end)
+    |> Enum.filter(&(!is_nil(&1)))
+    |> Enum.max(&>=/2, fn -> nil end)
+  end
+end
+
+tastiest = RecipeFinder.findTastiestRecipe(ingredientsWithoutCalories, 100, [0, 0, 0, 0])
+IO.puts("Tastiest: #{tastiest}")
+
+healthiest =
+  RecipeFinder.findTastiestRecipeWithExactCalories(ingredientsWithCalories, 100, 500, [0, 0, 0, 0])
+
+IO.puts("Healthiest: #{healthiest}")