My Advent of Code solutions in Python.
kevinyap.ca/2019/12/going-fast-in-advent-of-code/
advent-of-code
python
Add 2021/14
+47
+47
2021/day14.py
+47
2021/day14.py
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import fileinput
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from collections import Counter, defaultdict, deque, namedtuple # NOQA
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# Read problem input.
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data = ''.join([line for line in fileinput.input()])
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groups = [g.split('\n') for g in data.split('\n\n')]
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POLYMER = groups[0][0]
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MAPPING = {}
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for line in groups[1]:
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a, b = line.split(' -> ')
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MAPPING[a] = b
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# COUNTS maps bigrams to their counts in the underlying polymer.
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COUNTS = Counter()
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for i in range(len(POLYMER)-1):
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COUNTS[POLYMER[i:i+2]] += 1
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for iteration in range(1, 40 + 1):
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new_counts = Counter()
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for bigram, num in COUNTS.items():
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insertion = MAPPING[bigram]
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new_counts[bigram[0] + insertion] += num
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new_counts[insertion + bigram[1]] += num
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COUNTS = new_counts
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if iteration in (10, 40):
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# Compute counts of individual letters from bigram counts.
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letter_counts = Counter()
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for bigram, num in COUNTS.items():
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letter_counts[bigram[0]] += num
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letter_counts[bigram[1]] += num
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frequencies = zip(*letter_counts.most_common())[1]
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most = (frequencies[0] + 1) // 2
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least = (frequencies[-1] + 1) // 2
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print "Part 1:" if iteration == 10 else "Part 2:", most - least