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