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2 files changed, 56 insertions, 0 deletions

diff --git a/racket/aoc2021/day-02/day-02.ex b/racket/aoc2021/day-02/day-02.ex
new file mode 100644
index 0000000..d37ab05
--- /dev/null
+++ b/racket/aoc2021/day-02/day-02.ex
@@ -0,0 +1,32 @@
+defmodule Day02 do
+  def part_one(data) do
+    data
+    |> Enum.reduce(%{pos: 0, dep: 0}, &method_one/2)
+    |> get_answer()
+  end
+
+  def part_two(data) do
+    data
+    |> Enum.reduce(%{pos: 0, dep: 0, aim: 0}, &method_two/2)
+    |> get_answer()
+  end
+
+  defp method_one({:forward, x}, s), do: %{s | pos: s.pos + x}
+  defp method_one({:up, x}, s), do: %{s | dep: s.dep - x}
+  defp method_one({:down, x}, s), do: %{s | dep: s.dep + x}
+
+  defp method_two({:forward, x}, s), do: %{s | pos: s.pos + x, dep: s.dep + s.aim * x}
+  defp method_two({:up, x}, s), do: %{s | aim: s.aim - x}
+  defp method_two({:down, x}, s), do: %{s | aim: s.aim + x}
+
+  defp get_answer(s), do: s.pos * s.dep
+end
+
+data =
+  File.read!("day-02/input.txt")
+  |> String.split("\n", trim: true)
+  |> Enum.map(&String.split/1)
+  |> Enum.map(fn [dir, amt] -> {String.to_atom(dir), String.to_integer(amt)} end)
+
+Day02.part_one(data) |> IO.inspect()
+Day02.part_two(data) |> IO.inspect()
diff --git a/racket/aoc2021/day-02/day-02.rkt b/racket/aoc2021/day-02/day-02.rkt
new file mode 100644
index 0000000..0bd0c3d
--- /dev/null
+++ b/racket/aoc2021/day-02/day-02.rkt
@@ -0,0 +1,24 @@
+#lang racket
+(require advent-of-code
+         threading
+         algorithms)
+
+(define motion-data
+  (~> (open-aoc-input (find-session) 2021 2 #:cache (string->path "./cache"))
+      (port->list read _)
+      (chunks-of _ 2)))
+
+;; part 1
+(for/fold ([depth 0] [position 0] #:result (* depth position)) ([motion (in-list motion-data)])
+  (match motion
+    [(list 'forward x) (values depth (+ position x))]
+    [(list 'up x) (values (- depth x) position)]
+    [(list 'down x) (values (+ depth x) position)]))
+
+;; part 2
+(for/fold ([aim 0] [depth 0] [position 0] #:result (* depth position))
+          ([motion (in-list motion-data)])
+  (match motion
+    [(list 'forward x) (values aim (+ depth (* aim x)) (+ position x))]
+    [(list 'up x) (values (- aim x) depth position)]
+    [(list 'down x) (values (+ aim x) depth position)]))