Add day12

Signed-off-by: Alek Ratzloff <alekratz@gmail.com>

day12/day12.py

@@ -0,0 +1,87 @@
+#!/usr/bin/env python3
+import sys
+from collections import defaultdict
+from copy import deepcopy
+from typing import DefaultDict, MutableMapping, Set
+import pprint
+import string
+
+
+Vertices = DefaultDict[str, Set[str]]
+SMALL = set(string.ascii_lowercase)
+BIG = set(string.ascii_uppercase)
+
+
+def is_small(cave: str):
+    s = set(cave)
+    return (s & SMALL) == s
+
+
+def part1(vertices: Vertices):
+    small = {cave for cave in vertices.keys() if is_small(cave)}
+    big = set(vertices.keys()) - small
+    assert len(big & small) == 0
+
+    def find_paths(current: str, visited: Set[str] = set(), path: str = "") -> Set[str]:
+        visited = deepcopy(visited)
+        visited |= {current}
+        paths = set()
+        for vertex in vertices[current]:
+            if vertex == "end":
+                paths |= {path}
+            elif vertex in visited and vertex in small:
+                continue
+            else:
+                paths |= find_paths(vertex, visited, path + vertex)
+        return paths
+
+    paths = find_paths("start")
+    print(len(paths))
+
+
+def part2(vertices: Vertices):
+    small = {cave for cave in vertices.keys() if is_small(cave)}
+    big = set(vertices.keys()) - small
+    assert len(big & small) == 0
+
+    def find_paths(
+        allowed: str,
+        current: str,
+        visited: MutableMapping[str, int] = defaultdict(lambda: 0),
+        path: str = "",
+    ) -> Set[str]:
+        if current == allowed:
+            if visited[current] >= 2:
+                # This is a small cave and we've already visited it twice
+                return set()
+        elif current in small and visited[current]:
+            # Visited already
+            return set()
+        visited = deepcopy(visited)
+        visited[current] += 1
+        paths = set()
+        for vertex in vertices[current]:
+            if vertex == "end":
+                paths |= {path}
+            else:
+                paths |= find_paths(allowed, vertex, visited, path + vertex)
+        return paths
+
+    paths = set()
+    for allowed in small - {"start", "end"}:
+        paths |= find_paths(allowed, "start")
+    print(len(paths))
+
+
+# Doing this comprehension so Mypy is happy
+edges = [(a, b) for a, b in map(lambda l: l.strip().split("-"), sys.stdin)]
+vertices: Vertices = defaultdict(set)
+for a, b in edges:
+    vertices[a] |= {b}
+    vertices[b] |= {a}
+
+
+print("Part 1")
+part1(vertices)
+print("Part 2")
+part2(vertices)