My Advent of Code solutions in Python.
kevinyap.ca/2019/12/going-fast-in-advent-of-code/
advent-of-code
python
Use deques for Day 19 Part 2
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2016/day19.py
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2016/day19.py
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def circular_elves(num_elves):
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seen = set()
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victim = num_elves // 2
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left = deque(range(1, (num_elves // 2) + 1))
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right = deque(range((num_elves // 2) + 1, num_elves + 1))
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# Start with a double jump if number of elves is odd
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double = (num_elves % 2) == 1
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while len(left) + len(right) > 1:
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# Remove the middle Elf in the circle
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right.popleft()
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while True:
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seen.add(victim)
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# Move an Elf from between deques
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right.append(left.popleft())
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if len(seen) == num_elves:
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return victim + 1
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for _ in range(2 if double else 1):
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victim = (victim + 1) % num_elves
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while victim in seen:
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victim = (victim + 1) % num_elves
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# Rebalance the deques if uneven
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if len(right) - len(left) == 2:
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left.append(right.popleft())
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double = not double
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return right[0]
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if __name__ == '__main__':