From 1d06b5bdb5862a13510e2683059c876839c02449 Mon Sep 17 00:00:00 2001
From: Bruno BELANYI <bruno@belanyi.fr>
Date: Sun, 12 Dec 2021 15:12:36 +0100
Subject: [PATCH 1/4] 2021: d12: ex1: add input

---
 2021/d12/ex1/input | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)
 create mode 100644 2021/d12/ex1/input

diff --git a/2021/d12/ex1/input b/2021/d12/ex1/input
new file mode 100644
index 0000000..c2b0b8d
--- /dev/null
+++ b/2021/d12/ex1/input
@@ -0,0 +1,22 @@
+ax-end
+xq-GF
+end-xq
+im-wg
+ax-ie
+start-ws
+ie-ws
+CV-start
+ng-wg
+ng-ie
+GF-ng
+ng-av
+CV-end
+ie-GF
+CV-ie
+im-xq
+start-GF
+GF-ws
+wg-LY
+CV-ws
+im-CV
+CV-wg

From 4e46f615cf078f2204f607f451a880a1d7cfc75c Mon Sep 17 00:00:00 2001
From: Bruno BELANYI <bruno@belanyi.fr>
Date: Sun, 12 Dec 2021 15:13:10 +0100
Subject: [PATCH 2/4] 2021: d12: ex1: add solution

---
 2021/d12/ex1/ex1.py | 46 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 46 insertions(+)
 create mode 100755 2021/d12/ex1/ex1.py

diff --git a/2021/d12/ex1/ex1.py b/2021/d12/ex1/ex1.py
new file mode 100755
index 0000000..4d0cacf
--- /dev/null
+++ b/2021/d12/ex1/ex1.py
@@ -0,0 +1,46 @@
+#!/usr/bin/env python
+
+import itertools
+import sys
+from collections import defaultdict
+from typing import Dict, List, Set
+
+Map = Dict[str, Set[str]]
+
+
+def solve(input: List[str]) -> int:
+    def parse() -> Map:
+        res: Map = defaultdict(set)
+
+        for (start, to) in map(lambda s: s.split("-"), input):
+            res[start].add(to)
+            res[to].add(start)
+
+        return res
+
+    caves = parse()
+
+    def dfs(start: str, seen: Set[str] = set()) -> int:
+        if start == "end":
+            return 1
+
+        seen = seen | {start}
+        res = 0
+
+        for dest in caves[start]:
+            if dest in seen and dest.islower():
+                continue
+            res += dfs(dest, seen)
+
+        return res
+
+    return dfs("start")
+
+
+def main() -> None:
+    input = [line.strip() for line in sys.stdin.readlines()]
+    print(solve(input))
+
+
+if __name__ == "__main__":
+    main()

From 50ee5d1a50ed3c8a9fc35a2aeefa6777337d334e Mon Sep 17 00:00:00 2001
From: Bruno BELANYI <bruno@belanyi.fr>
Date: Sun, 12 Dec 2021 15:13:21 +0100
Subject: [PATCH 3/4] 2021: d12: ex2: add input

---
 2021/d12/ex2/input | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)
 create mode 100644 2021/d12/ex2/input

diff --git a/2021/d12/ex2/input b/2021/d12/ex2/input
new file mode 100644
index 0000000..c2b0b8d
--- /dev/null
+++ b/2021/d12/ex2/input
@@ -0,0 +1,22 @@
+ax-end
+xq-GF
+end-xq
+im-wg
+ax-ie
+start-ws
+ie-ws
+CV-start
+ng-wg
+ng-ie
+GF-ng
+ng-av
+CV-end
+ie-GF
+CV-ie
+im-xq
+start-GF
+GF-ws
+wg-LY
+CV-ws
+im-CV
+CV-wg

From 8e030c9d88d5b2ec9e4f4500f05942b85da5a65c Mon Sep 17 00:00:00 2001
From: Bruno BELANYI <bruno@belanyi.fr>
Date: Sun, 12 Dec 2021 15:13:41 +0100
Subject: [PATCH 4/4] 2021: d12: ex2: add solution

---
 2021/d12/ex2/ex2.py | 49 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 49 insertions(+)
 create mode 100755 2021/d12/ex2/ex2.py

diff --git a/2021/d12/ex2/ex2.py b/2021/d12/ex2/ex2.py
new file mode 100755
index 0000000..69d9aa9
--- /dev/null
+++ b/2021/d12/ex2/ex2.py
@@ -0,0 +1,49 @@
+#!/usr/bin/env python
+
+import itertools
+import sys
+from collections import defaultdict
+from typing import Dict, List, Set
+
+Map = Dict[str, Set[str]]
+
+
+def solve(input: List[str]) -> int:
+    def parse() -> Map:
+        res: Map = defaultdict(set)
+
+        for (start, to) in map(lambda s: s.split("-"), input):
+            res[start].add(to)
+            res[to].add(start)
+
+        return res
+
+    caves = parse()
+
+    def dfs(start: str, seen: Set[str] = set(), has_doubled_back: bool = False) -> int:
+        if start == "end":
+            return 1
+
+        seen = seen | {start}
+        res = 0
+
+        for dest in caves[start]:
+            doubles_back = False
+            if dest in seen and dest.islower():
+                if has_doubled_back or dest == "start":
+                    continue
+                doubles_back = True
+            res += dfs(dest, seen, has_doubled_back or doubles_back)
+
+        return res
+
+    return dfs("start")
+
+
+def main() -> None:
+    input = [line.strip() for line in sys.stdin.readlines()]
+    print(solve(input))
+
+
+if __name__ == "__main__":
+    main()