Day 12

day12/input.txt

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+CV-mk
+gm-IK
+sk-gm
+ca-sk
+sx-mk
+gm-start
+sx-ca
+kt-sk
+ca-VS
+kt-ml
+kt-ca
+mk-IK
+end-sx
+end-sk
+gy-sx
+end-ca
+ca-ml
+gm-CV
+sx-kt
+start-CV
+IK-start
+CV-kt
+ml-mk
+ml-CV
+ml-gm
+ml-IK

day12/part1.py

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+#!/usr/bin/env python3
+from collections import defaultdict
+
+lines = (x.strip() for x in open("input.txt"))
+paths = defaultdict(set)
+stored_sum = {}
+
+for line in lines:
+    a, b = line.split("-")
+    paths[a].add(b)
+    paths[b].add(a)
+
+
+def visit(node, visited):
+    store_key = hash((node, frozenset(visited)))
+    if node == 'end':
+        return 1
+    elif store_key not in stored_sum:
+        stored_sum[store_key] = sum(
+            visit(nxt, visited.union([nxt]) if nxt != nxt.upper() else visited)
+            for nxt in paths[node].difference(visited)
+        )
+    return stored_sum[store_key]
+
+
+
+print(visit('start', {'start'}))

day12/part2.py

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+#!/usr/bin/env python3
+from collections import defaultdict
+
+lines = (x.strip() for x in open("input.txt"))
+paths = defaultdict(set)
+stored_sum = {}
+
+for line in lines:
+    a, b = line.split("-")
+    paths[a].add(b)
+    paths[b].add(a)
+
+
+def visit(node, visited):
+    store_key = hash((node, frozenset(hash((k, v)) for k, v in visited.items())))
+    if node == 'end':
+        return 1
+    elif store_key not in stored_sum:
+        has_twice = max(visited.values()) > 1
+        stored_sum[store_key] = sum(
+            visit(nxt, {**visited, nxt: visited.get(nxt, 0) + 1} if nxt != nxt.upper() else visited)
+            for nxt in paths[node].difference(
+                set(k for k, v in visited.items() if v >= (1 if has_twice else 2) or (v == 1 and k == 'start'))
+            )
+        )
+    return stored_sum[store_key]
+
+
+print(visit('start', {'start': 1}))