58 lines
1.4 KiB
Python
58 lines
1.4 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 typing import Dict, Iterator, List, Tuple, TypeVar
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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[str, Rules]:
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template = 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, rules
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def step(template: str, rules: Rules) -> str:
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res: List[str] = []
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# Look at all pairs
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for a, b in zip(template, template[1:]):
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res.append(a)
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if (a + b) in rules:
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res.append(rules[a + b])
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# Add the last element
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res.append(template[-1])
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return "".join(res)
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def polymerize(template: str, rules: Rules) -> Iterator[str]:
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while True:
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yield (template := step(template, rules))
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def score(template: str) -> int:
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counts = [n for __, n in Counter(template).most_common()]
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return counts[0] - counts[-1]
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template, rules = parse()
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return score(nth(polymerize(template, rules), 10 - 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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