Solve 2021 Day 7 part 2 in elixir

2021/Day7/Elixir/whales.ex

@@ -10,6 +10,12 @@ defmodule Whales do
 
   def distance_to(a, b), do: abs(a - b)
 
+  def increasing_distance_to(a, b) do
+    1..abs(a - b)
+    |> Enum.to_list()
+    |> Enum.sum()
+  end
+
   def find_cheapest_route(positions),
     do: find_cheapest_route(positions, Enum.min(positions), nil)
 
@@ -37,6 +43,37 @@ defmodule Whales do
     end
   end
 
+  def find_new_cheapest_route(positions),
+    do: find_new_cheapest_route(positions, Enum.min(positions), nil)
+
+  def find_new_cheapest_route(positions, target, cheapest) do
+    # This takes a while, so we add debug output
+    IO.inspect(target, label: "Target")
+    IO.inspect(Enum.count(positions), label: "Positions")
+
+    if target >= Enum.count(positions) + 1 do
+      cheapest
+    else
+      current =
+        if target == Enum.max(positions) + 1 do
+          cheapest
+        else
+          positions
+          |> Enum.map(fn position -> increasing_distance_to(position, target) end)
+          |> Enum.sum()
+        end
+
+      new_cheapest =
+        if current < cheapest do
+          current
+        else
+          cheapest
+        end
+
+      find_new_cheapest_route(positions, target + 1, new_cheapest)
+    end
+  end
+
   @spec first() :: Integer
   def first() do
     positions = load_file("../input.txt")
@@ -45,6 +82,8 @@ defmodule Whales do
 
   @spec second() :: Integer
   def second() do
+    positions = load_file("../input.txt")
+    find_new_cheapest_route(positions)
   end
 end