3 files changed, 74 insertions, 0 deletions
diff --git a/2021/12/Makefile b/2021/12/Makefile
new file mode 100644
index 0000000..247194a
--- /dev/null
+++ b/2021/12/Makefile
@@ -0,0 +1,8 @@
+all:
+	sed '/START PART 2/,/END PART 2/d' puzzles.py >puzzle-1.py
+	sed '/START PART 1/,/END PART 1/d' puzzles.py >puzzle-2.py
+	chmod +x puzzle-[12].py
+
+.PHONY: clean
+clean:
+	rm -f puzzle-[12].py
diff --git a/2021/12/input b/2021/12/input
new file mode 100644
index 0000000..1cacb23
--- /dev/null
+++ b/2021/12/input
@@ -0,0 +1,25 @@
+qi-UD
+jt-br
+wb-TF
+VO-aa
+UD-aa
+br-end
+end-HA
+qi-br
+br-HA
+UD-start
+TF-qi
+br-hf
+VO-hf
+start-qi
+end-aa
+hf-HA
+hf-UD
+aa-hf
+TF-hf
+VO-start
+wb-aa
+UD-wb
+KX-wb
+qi-VO
+br-TF
diff --git a/2021/12/puzzles.py b/2021/12/puzzles.py
new file mode 100644
index 0000000..8cfc506
--- /dev/null
+++ b/2021/12/puzzles.py
@@ -0,0 +1,41 @@
+#!/usr/bin/env python3
+
+from collections import defaultdict
+
+
+def solve(paths: defaultdict[list[str]], path: str) -> int:
+	acc = 0
+	tokens = path[0].split(",")
+
+	for dest in paths[tokens[-1]]:
+		if dest == "end":
+			acc += 1
+		# START PART 1
+		elif not (dest.islower() and dest in tokens):
+			acc += solve(paths, (f"{path[0]},{dest}", False))
+		# END PART 1 START PART 2
+		elif dest != "start":
+			if dest.islower() and dest in tokens:
+				if path[1]:
+					continue
+				acc += solve(paths, (f"{path[0]},{dest}", True))
+			else:
+				acc += solve(paths, (f"{path[0]},{dest}", path[1]))
+		# END PART 2
+
+	return acc
+
+
+def main() -> None:
+	paths: defaultdict[list[str]] = defaultdict(list)
+	with open("input", "r", encoding="utf-8") as f:
+		for entry in f.readlines():
+			x, y = entry.strip().split("-")
+			paths[x].append(y)
+			paths[y].append(x)
+
+	print(solve(paths, ("start", False)))
+
+
+if __name__ == "__main__":
+	main()