My Advent of Code solutions in Python.
kevinyap.ca/2019/12/going-fast-in-advent-of-code/
advent-of-code
python
Add 2021/12
+45
+45
2021/day12.py
+45
2021/day12.py
···
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import copy
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import fileinput
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from collections import Counter, defaultdict
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graph = defaultdict(set)
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smalls = set()
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for line in fileinput.input():
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a, b = line.strip().split('-')
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graph[a].add(b)
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graph[b].add(a)
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def dfs(start, extra_time=False):
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num_paths = [0]
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def _dfs(node, seen=None, doubled=False):
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if seen is None:
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seen = Counter({'start': 1 if extra_time else 0})
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if node == 'end':
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num_paths[0] += 1
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return
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# If small cave, check if part 1/2 and skip accordingly.
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if node == node.lower():
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if (doubled or not extra_time) and seen[node] >= 1:
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return
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elif not doubled and seen[node] >= 2:
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return
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seen[node] += 1
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if node == node.lower() and node not in ('start', 'end') and seen[node] >= 2:
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doubled = True
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for n in graph[node]:
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_dfs(n, copy.deepcopy(seen), doubled=doubled)
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_dfs(start)
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return num_paths[0]
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print "Part 1:", dfs('start')
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print "Part 2:", dfs('start', extra_time=True)