My Advent of Code solutions in Python.
kevinyap.ca/2019/12/going-fast-in-advent-of-code/
advent-of-code
python
Add 2022/24
+106
+106
2022/day24.py
+106
2022/day24.py
···
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import fileinput
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from collections import deque
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from utils import Point, N, E, S, W
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def search(graph, start, goal):
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def gen_neighbours(node, depth):
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"""Returns all valid neighbours for a given node."""
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for n in node.neighbours_4():
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if graph.get(n, ' ') == '.':
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if n not in get_blizzard_locs(depth + 1):
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yield n
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if node not in get_blizzard_locs(depth + 1):
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yield node
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part_1 = None
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part_2 = None
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horizon = deque([(0, 0, start)]) # priority, checkpoint, node
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seen = set()
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while horizon:
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depth, checkpoint, curr = horizon.popleft()
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if (depth, checkpoint, curr) in seen:
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continue
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seen.add((depth, checkpoint, curr))
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# Reached the goal for the second time after making it back to the start.
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if curr == goal and checkpoint == 2:
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part_2 = depth
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print("Part 2:", part_2)
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return part_1, part_2
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# Reached the goal for the first time.
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elif curr == goal and checkpoint == 0:
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if part_1 is None:
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part_1 = depth
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print("Part 1:", part_1)
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checkpoint = 1
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# Reached the start after touching the goal the first time.
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elif curr == start and checkpoint == 1:
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checkpoint = 2
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for n in gen_neighbours(curr, depth):
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horizon.append((depth + 1, checkpoint, n))
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# N and S are swapped because of positive-Y direction convention.
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MAPPING = {
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'v': N,
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'>': E,
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'^': S,
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'<': W,
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}
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BLIZZARDS = {}
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BLIZZARD_LOCS = {}
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def get_blizzard_locs(step):
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"""Returns the set of all blizzard positions for the given time step."""
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if step in BLIZZARDS:
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return BLIZZARD_LOCS[step]
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last_blizzards = BLIZZARDS[step - 1]
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new_blizzards = []
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for p, b in last_blizzards:
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np = p + MAPPING[b]
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if BOARD.get(np) == '#':
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np = p
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while BOARD.get(np) != '#':
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np -= MAPPING[b]
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np += MAPPING[b]
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new_blizzards.append((np, b))
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BLIZZARDS[step] = new_blizzards
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BLIZZARD_LOCS[step] = set(p for p, _ in new_blizzards)
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return BLIZZARD_LOCS[step]
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# Read problem input.
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BOARD = {}
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BLIZZARDS = {0: []}
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START = None
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GOAL = None
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for y, line in enumerate(fileinput.input()):
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for x, c in enumerate(line.strip()):
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p = Point(x, y)
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if c == '.':
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if y == 0:
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START = p
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GOAL = p
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BOARD[p] = '.'
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elif c in MAPPING:
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BLIZZARDS[0].append((p, c))
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BOARD[p] = '.'
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else:
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BOARD[p] = '#'
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# Solve problem.
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search(BOARD, START, GOAL)