67 lines
1.8 KiB
Python
67 lines
1.8 KiB
Python
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#!/usr/bin/env python
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import itertools
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import sys
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from collections import Counter
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from copy import deepcopy
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from typing import Dict, Iterator, List, NamedTuple, Tuple, TypeVar
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class Template(NamedTuple):
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bigrams: Counter[str]
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counts: Counter[str]
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Rules = Dict[str, str]
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T = TypeVar("T")
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def nth(iterable: Iterator[T], n: int) -> T:
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return next(itertools.islice(iterable, n, None))
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def solve(input: List[str]) -> int:
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def parse() -> Tuple[Template, Rules]:
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bigrams = Counter(a + b for a, b in zip(input[0], input[0][1:]))
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counts = Counter(input[0])
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rules = {
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pair: insertion
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for pair, insertion in map(lambda s: s.split(" -> "), input[2:])
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}
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return Template(bigrams, counts), rules
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def step(template: Template, rules: Rules) -> Template:
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bigrams: Counter[str] = Counter()
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counts = deepcopy(template.counts)
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for p, n in template.bigrams.items():
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if p in rules:
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insertion = rules[p]
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bigrams[p[0] + insertion] += n
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bigrams[insertion + p[1]] += n
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counts[insertion] += n
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else:
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# Counts are not changed in this case
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bigrams[p] = n
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return Template(bigrams, counts)
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def polymerize(template: Template, rules: Rules) -> Iterator[Template]:
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while True:
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yield (template := step(template, rules))
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def score(template: Template) -> int:
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nums = [n for __, n in template.counts.most_common()]
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return nums[0] - nums[-1]
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template, rules = parse()
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return score(nth(polymerize(template, rules), 40 - 1))
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def main() -> None:
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input = [line.strip() for line in sys.stdin.readlines()]
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print(solve(input))
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if __name__ == "__main__":
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main()
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