From 0473bf6da259e41029a0d547feb163b3d84e38d0 Mon Sep 17 00:00:00 2001
From: Pascal Lais <pascal@lais.dev>
Date: Sun, 12 Dec 2021 22:10:55 +0100
Subject: [PATCH] Add day 12 solution

---
 day-12/day-12.py | 79 ++++++++++++++++++++++++++++++++++++++++++++++++
 day-12/input.txt | 24 +++++++++++++++
 2 files changed, 103 insertions(+)
 create mode 100644 day-12/day-12.py
 create mode 100644 day-12/input.txt

diff --git a/day-12/day-12.py b/day-12/day-12.py
new file mode 100644
index 0000000..b201f47
--- /dev/null
+++ b/day-12/day-12.py
@@ -0,0 +1,79 @@
+#!/usr/bin/env python3
+from pathlib import Path
+
+
+def process_node(node, available_edges, visited):
+    paths = []
+    if node == "end":
+        return [[node]]
+    if node.islower():
+        visited.add(node)
+    neighbors = [[n for n in e if n != node]
+                 for e in available_edges if node in e]
+    for n in neighbors:
+        n = n[0]
+        if n not in visited:
+            next = process_node(n, available_edges, visited)
+            for p in next:
+                paths.append([node] + p)
+    if node in visited:
+        visited.remove(node)
+    return paths
+
+
+def process_node_twice(node, available_edges, visited, twice):
+    paths = []
+    if node == "end":
+        return [[node]]
+    if node.islower():
+        if node in visited and twice:
+            return paths
+        elif node in visited and node != "start":
+            twice = node
+        else:
+            visited.add(node)
+    neighbors = [[n for n in e if n != node]
+                 for e in available_edges if node in e]
+    for n in neighbors:
+        n = n[0]
+        if n not in visited or twice != node and n != "start":
+            next = process_node_twice(n, available_edges, visited, twice)
+            for p in next:
+                paths.append([node] + p)
+    if twice == node:
+        twice = ""
+    elif node in visited:
+        visited.remove(node)
+    return paths
+
+
+def part_1(input):
+    result = 0
+    edges = []
+    for line in input:
+        n_start, n_end = line.strip().split('-')
+        e = (n_start, n_end)
+        edges.append(e)
+    paths = process_node("start", edges, set())
+    result = len(paths)
+    print("Part 1 result:", result)
+
+
+def part_2(input):
+    result = 0
+    edges = []
+    for line in input:
+        n_start, n_end = line.strip().split('-')
+        e = (n_start, n_end)
+        edges.append(e)
+    paths = process_node_twice("start", edges, set(), "")
+    result = len(paths)
+    print("Part 2 result:", result)
+
+
+input = list()
+p = Path(__file__).with_name('input.txt')
+with open(p) as f:
+    input = f.readlines()
+    part_1(input)
+    part_2(input)
diff --git a/day-12/input.txt b/day-12/input.txt
new file mode 100644
index 0000000..aee752f
--- /dev/null
+++ b/day-12/input.txt
@@ -0,0 +1,24 @@
+pf-pk
+ZQ-iz
+iz-NY
+ZQ-end
+pf-gx
+pk-ZQ
+ZQ-dc
+NY-start
+NY-pf
+NY-gx
+ag-ZQ
+pf-start
+start-gx
+BN-ag
+iz-pf
+ag-FD
+pk-NY
+gx-pk
+end-BN
+ag-pf
+iz-pk
+pk-ag
+iz-end
+iz-BN
\ No newline at end of file