From 9fb42bf830560502aaf5acb3241c3bc8b53a35c2 Mon Sep 17 00:00:00 2001
From: Justin Wernick <justin@worthe-it.co.za>
Date: Sun, 20 Oct 2024 18:01:18 +0200
Subject: Day 23

---
 2015/day23.exs | 57 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 57 insertions(+)
 create mode 100644 2015/day23.exs

(limited to '2015')

diff --git a/2015/day23.exs b/2015/day23.exs
new file mode 100644
index 0000000..433f70a
--- /dev/null
+++ b/2015/day23.exs
@@ -0,0 +1,57 @@
+require Integer
+
+program =
+  File.stream!("inputs/day23.txt")
+  |> Enum.map(&String.trim(&1))
+
+programLength = length(program)
+
+step = fn {programCounter, a, b} ->
+  instruction = Enum.at(program, programCounter)
+
+  case instruction do
+    "hlf a" ->
+      {programCounter + 1, div(a, 2), b}
+
+    "tpl a" ->
+      {programCounter + 1, a * 3, b}
+
+    "inc a" ->
+      {programCounter + 1, a + 1, b}
+
+    "inc b" ->
+      {programCounter + 1, a, b + 1}
+
+    <<"jmp " <> offset::binary>> ->
+      {offset, ""} = Integer.parse(offset)
+      {programCounter + offset, a, b}
+
+    <<"jie a, " <> offset::binary>> ->
+      if Integer.is_even(a) do
+        {offset, ""} = Integer.parse(offset)
+        {programCounter + offset, a, b}
+      else
+        {programCounter + 1, a, b}
+      end
+
+    <<"jio a, " <> offset::binary>> ->
+      if a == 1 do
+        {offset, ""} = Integer.parse(offset)
+        {programCounter + offset, a, b}
+      else
+        {programCounter + 1, a, b}
+      end
+  end
+end
+
+{_, _, terminalState1} =
+  Stream.iterate({0, 0, 0}, &step.(&1))
+  |> Enum.find(fn {programCounter, _, _} -> programCounter >= programLength end)
+
+IO.puts("Part 1: #{terminalState1}")
+
+{_, _, terminalState2} =
+  Stream.iterate({0, 1, 0}, &step.(&1))
+  |> Enum.find(fn {programCounter, _, _} -> programCounter >= programLength end)
+
+IO.puts("Part 2: #{terminalState2}")
-- 
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