wip: 2015 day 24

2015/lib/2015/24.ex

@@ -0,0 +1,53 @@
+import AOC
+
+aoc 2015, 24 do
+  def p1 do
+    packages = read_packages()
+    target = packages |> Enum.sum() |> div(3)
+
+    distribute_packages(packages, target, List.duplicate([], 3))
+  end
+
+  def p2 do
+  end
+
+  ## solution
+
+  def distribute_packages(nums, bin_count) do
+    target =
+      nums
+      |> Enum.sum()
+      |> div(bin_count)
+
+    bins = List.duplicate([], bin_count)
+
+    distribute_packages(nums, target, bins)
+  end
+
+  def distribute_packages([], target, bins) do
+    if Enum.all?(bins, &(Enum.sum(&1) == target)) do
+      [bins]
+    else
+      []
+    end
+  end
+
+  def distribute_packages([n | rest], target, bins) do
+    if Enum.any?(bins, &(Enum.sum(&1) > target)) do
+      []
+    else
+      Enum.flat_map(0..(length(bins) - 1), fn i ->
+        updated_bins = List.update_at(bins, i, &[n | &1])
+        distribute_packages(rest, target, updated_bins)
+      end)
+    end
+  end
+
+  ## input
+
+  defp read_packages do
+    input_string()
+    |> String.split("\n", trim: true)
+    |> Enum.map(&String.to_integer/1)
+  end
+end