day09

Author: akdemironur

09/sample_input

@@ -0,0 +1,3 @@
+0 3 6 9 12 15
+1 3 6 10 15 21
+10 13 16 21 30 45

09/sol.exs

@@ -0,0 +1,39 @@
+defmodule Day09 do
+  defp read_input(file_path) do
+    case File.read(file_path) do
+      {:ok, content} ->
+        content
+        |> String.split("\n", trim: true)
+        |> Enum.map(&String.split(&1, " ", trim: true))
+        |> Enum.map(fn x -> Enum.map(x, &String.to_integer/1) end)
+
+      {:error, reason} ->
+        raise "Oh no! #{reason}"
+    end
+  end
+
+  defp extrapolate(xs) do
+    if Enum.all?(xs, fn x -> x == 0 end) do
+      0
+    else
+      0..(length(xs) - 2)
+      |> Enum.map(fn i -> Enum.at(xs, i + 1) - Enum.at(xs, i) end)
+      |> (&(hd(Enum.take(xs, -1)) + extrapolate(&1))).()
+    end
+  end
+
+  def partA(file_path) do
+    read_input(file_path)
+    |> Enum.map(&extrapolate/1)
+    |> Enum.sum()
+  end
+
+  def partB(file_path) do
+    read_input(file_path)
+    |> Enum.map(&extrapolate(Enum.reverse(&1)))
+    |> Enum.sum()
+  end
+end
+
+IO.puts(Day09.partA("./input"))
+IO.puts(Day09.partB("./input"))