My Advent of Code solutions in Python.
kevinyap.ca/2019/12/going-fast-in-advent-of-code/
advent-of-code
python
Add solution for 2023/08
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2023/day08.py
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2023/day08.py
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import fileinput
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from itertools import cycle
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from functools import reduce
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from utils import parse_line, lcm
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# Parse input.
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elements = {}
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for i, line in enumerate(fileinput.input()):
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if i == 0:
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instructions = line.strip()
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elif i >= 2:
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node, left, right = parse_line(r'(.+) = \((.+), (.+)\)', line)
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elements[node] = (left, right)
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# Solve part 1.
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curr = 'AAA'
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for i, ins in enumerate(cycle(instructions), start=1):
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if ins == 'L':
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curr = elements[curr][0]
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else:
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curr = elements[curr][1]
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if curr == 'ZZZ':
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print("Part 1:", i)
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break
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# Solve part 2.
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starts = [n for n in elements if n.endswith('A')]
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cycles = []
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for start in starts:
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curr = start
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seen = {}
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for i, ins in enumerate(cycle(instructions), start=1):
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if ins == 'L':
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curr = elements[curr][0]
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else:
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curr = elements[curr][1]
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if curr.endswith('Z'):
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if curr in seen:
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cycles.append(i - seen[curr])
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break
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seen[curr] = i
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i += 1
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print("Part 2:", int(reduce(lcm, cycles, 1)))
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