Day 8

lib/day8/day8.ex

@@ -0,0 +1,82 @@
+defmodule Day8 do
+  def create_node(numbers, indent \\ "") do
+    # IO.puts "#{indent}numbers: #{numbers |> Enum.join(", ")}"
+
+    [children_count, meta_count | numbers] = numbers
+
+    {children, numbers} =
+      if children_count > 0 do
+        IO.puts("#{indent}creating #{children_count} children")
+        Enum.reduce(1..children_count, {[], numbers}, fn child, {children, numbers} ->
+          IO.puts "#{indent}creating child #{child}"
+          {child, numbers} = create_node(numbers, indent <> "  ")
+          {
+            [child | children],
+            numbers
+          }
+        end)
+      else
+        {[], numbers}
+      end
+
+    {metadata, numbers} = 
+      if meta_count > 0 do
+        {
+          Enum.slice(numbers, 0, meta_count),
+          Enum.slice(numbers, meta_count..-1)
+        }
+      else
+        {[], numbers}
+      end
+
+    IO.puts "#{indent}metadata: #{metadata |> Enum.join(", ")}"
+
+    {
+      {children |> Enum.reverse(), metadata},
+      numbers
+    }
+  end
+
+  def sum_metadata({[], metadata}), do: Enum.sum(metadata)
+  def sum_metadata({children, metadata}) do
+    children_sum = Enum.map(children, &sum_metadata/1) |> Enum.sum()
+    children_sum + Enum.sum(metadata)
+  end
+
+  def node_value({children, metadata}) when length(children) == 0 do
+    Enum.sum(metadata)
+  end
+  def node_value({children, metadata}) do
+    # IO.inspect(children)
+    metadata
+    # |> IO.inspect
+    |> Enum.map(fn index ->
+      # IO.inspect(index - 1)
+      case Enum.fetch(children, index - 1) do
+        {:ok, child} -> node_value(child)
+        :error -> 0
+      end
+    end)
+    |> Enum.sum()
+  end
+
+  def parse_input() do
+    File.read!("lib/day8/input.txt")
+    |> String.split(" ", trim: true)
+    |> Enum.map(&String.to_integer/1)
+  end
+
+  def part1() do
+    {node, _numbers} =
+      parse_input()
+      |> create_node()
+    sum_metadata(node)
+  end
+
+  def part2() do
+    {node, _numbers} =
+      parse_input()
+      |> create_node()
+    node_value(node)
+  end
+end

test/day8_test.exs

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+defmodule Day8Test do
+  use ExUnit.Case
+  doctest Day8
+end