day 9

lib/advent_of_code/day_09.ex

@@ -1,7 +1,16 @@
 defmodule AdventOfCode.Day09 do
-  def part1(_args) do
+  alias Advent.D09_01
+  alias Advent.D09_02
+
+  def part1(inp) do
+    D09_01.parse_input(inp)
+    |> Enum.reduce(0, fn el, acc -> acc + (List.last(el) + D09_01.extrapolate(el, 0)) end)
   end
 
-  def part2(_args) do
+  def part2(inp) do
+    D09_01.parse_input(inp)
+    |> Enum.reduce(0, fn el, acc ->
+      acc + (List.first(el) - D09_02.get_left_val(D09_02.extrapolate(el, []), 0))
+    end)
   end
 end

lib/code/day9_1.ex

@@ -0,0 +1,33 @@
+defmodule Advent.D09_01 do
+  defp calc_next([], next), do: next
+
+  defp calc_next(curr, next) do
+    if(length(curr) > 1) do
+      [h | t] = curr
+      [h2 | _] = t
+      calc_next(t, [h - h2 | next])
+    else
+      next
+    end
+  end
+
+  def extrapolate(line, acc) do
+    if(Enum.all?(line, fn el -> el == 0 end)) do
+      acc
+    else
+      next = calc_next(Enum.reverse(line), [])
+      extrapolate(next, acc + List.last(next))
+    end
+  end
+
+  @sep "\n"
+  def parse_input(inp) do
+    inp
+    |> String.split(@sep, trim: true)
+    |> Enum.map(fn sublist ->
+      Enum.map(String.split(sublist, " ", trim: true), fn el ->
+        My.Utils.string_to_num_or_false(el)
+      end)
+    end)
+  end
+end

lib/code/day9_2.ex

@@ -0,0 +1,33 @@
+defmodule Advent.D09_02 do
+  defp calc_next([], next), do: next
+
+  defp calc_next(curr, next) do
+    if(length(curr) > 1) do
+      [h | t] = curr
+      [h2 | _] = t
+      calc_next(t, [h2 - h | next])
+    else
+      next
+    end
+  end
+
+  def extrapolate(line, res) do
+    if(Enum.all?(line, fn el -> el == 0 end)) do
+      res
+    else
+      next = Enum.reverse(calc_next(line, []))
+      extrapolate(next, [List.first(next)] ++ res)
+    end
+  end
+
+  def get_left_val([], acc), do: acc
+
+  def get_left_val(vals, acc) do
+    if(length(vals) > 0) do
+      [f | values] = vals
+      get_left_val(values, f - acc)
+    else
+      acc
+    end
+  end
+end

test/advent_of_code/day_09_test.exs

@@ -3,19 +3,24 @@ defmodule AdventOfCode.Day09Test do
 
   import AdventOfCode.Day09
 
-  @tag :skip
+  def test_input(),
+    do: """
+    0 3 6 9 12 15
+    1 3 6 10 15 21
+    10 13 16 21 30 45
+    """
+
   test "part1" do
-    input = nil
+    input = test_input()
     result = part1(input)
 
-    assert result
+    assert result == 114
   end
 
-  @tag :skip
   test "part2" do
-    input = nil
+    input = test_input()
     result = part2(input)
 
-    assert result
+    assert result == 2
   end
 end