33 lines
1.2 KiB
Python
33 lines
1.2 KiB
Python
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from collections import defaultdict
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from math import ceil
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with open("input14.txt") as f:
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lines = [line.rstrip() for line in f]
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template = lines[0]
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rules = {k: v for k, v in map(lambda s: s.split(" -> "), lines[2:])}
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pairs = defaultdict(int)
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for i in range(len(template) - 1):
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pairs[template[i:i+2]] += 1
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# N B B B C N C C N B B N B N B B C H B H H B C H B
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# NB BB BB BC CN NC CC CN NB BB BN NB BN NB BB BC CH HB BH HH HB BC CH HB
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# N=5, B=11, C=5, H=4, but in pairs N=9, B=21, C=10, H=8
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# so if odd: n+1 / 2 elif even: n / 2, which is ceil(n / 2) for both
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for step in range(40):
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for pair, n in list(pairs.items()):
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if pairs[pair] == 0:
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continue
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mid = rules[pair]
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new_pair1, new_pair2 = pair[0] + mid, mid + pair[1]
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pairs[pair] -= n
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pairs[new_pair1] += n
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pairs[new_pair2] += n
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if step in (9, 39):
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pcount = defaultdict(int)
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for pair, n in pairs.items():
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for p in pair:
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pcount[p] += n
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tcount = {p: ceil(n / 2) for p, n in pcount.items()}
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most_common = max(tcount, key=lambda p: tcount[p])
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least_common = min(tcount, key=lambda p: tcount[p])
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print(tcount[most_common] - tcount[least_common])
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