My Advent of Code solutions in Python.
kevinyap.ca/2019/12/going-fast-in-advent-of-code/
advent-of-code
python
Add 2022/09
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+58
2022/day09.py
+58
2022/day09.py
···
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import fileinput
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from utils import Point
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def sign(x, y):
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if x > y:
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return 1
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elif x < y:
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return -1
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else:
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return 0
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def update(head, tail):
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"""
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Given the current position of head and tail,
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return the new tail position.
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"""
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# This occurs if we have moved diagonally away from the tail,
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# and it is far enough for the tail to come and chase us.
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if abs(head.x - tail.x) + abs(head.y - tail.y) > 2:
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tail += Point(sign(head.x, tail.x), sign(head.y, tail.y))
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# Check if we need to move horizontally/vertically.
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elif (head.x == tail.x or head.y == tail.y) and (abs(head.x - tail.x) + abs(head.y - tail.y) > 1):
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tail += Point(sign(head.x, tail.x), sign(head.y, tail.y))
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return tail
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mapping = {
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"U": Point(0, 1),
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"R": Point(1, 0),
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"D": Point(0, -1),
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"L": Point(-1, 0),
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}
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INSTRUCTIONS = [line.strip() for line in fileinput.input()]
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# Solve problem.
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for part, bridge_len in ((1, 2), (2, 10)):
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bridge = [Point(0, 0) for _ in range(bridge_len)]
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seen = set()
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for line in INSTRUCTIONS:
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d, amt = line.split()
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amt = int(amt)
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for _ in range(amt):
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# First, move the head in the given direction.
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bridge[0] += mapping[d]
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for i in range(1, bridge_len):
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bridge[i] = update(bridge[i-1], bridge[i])
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seen.add(bridge[-1])
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print(f"Part {part}: {len(seen)}")
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