Add day 12 solution

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)