My Advent of Code solutions in Python.
kevinyap.ca/2019/12/going-fast-in-advent-of-code/
advent-of-code
python
Add solution for 2023/17
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+72
2023/day17.py
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2023/day17.py
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import fileinput
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import heapq
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from utils import Point, DIRS, N, S, E, W
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def minimize_heat_loss(graph, start, goal=None, part_2=False):
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def gen_neighbours(node, hist):
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for d in DIRS:
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n = node + d
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if n not in graph:
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continue
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if hist:
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# No U-turns allowed.
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if hist[-1] == -d:
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continue
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if part_2:
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# Early ultra crucible turn.
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if len(hist) < 4 and d != hist[-1]:
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continue
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# Early ultra crucible turn.
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if len(set(hist[-4:])) != 1 and d != hist[-1]:
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continue
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# Wobbly ultra crucible.
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if len(hist) == 10 and all(x == d for x in hist):
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continue
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else:
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# Unstable regular crucible.
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if len(hist) >= 3 and all(x == d for x in hist[-3:]):
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continue
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yield n, graph[n], d
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horizon = [(0, start, ())]
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seen = set()
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buf_len = 10 if part_2 else 4
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while horizon:
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depth, curr, hist = heapq.heappop(horizon)
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if (curr, hist) in seen:
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continue
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seen.add((curr, hist))
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# Check if at the bottom-right, and that our last 4 moves
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# were in the same direction if we're solving part 2.
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if curr == goal and (not part_2 or len(set(hist[-4:])) == 1):
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return depth
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for neighbour, weight, nd in gen_neighbours(curr, hist):
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new_cost = weight + depth
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new_hist = hist + (nd,)
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heapq.heappush(horizon, (new_cost, neighbour, new_hist[-buf_len:]))
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# Read problem input.
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graph = {}
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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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graph[Point(x, y)] = int(c)
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start = Point(0, 0)
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end = Point(x, y)
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# Solve problem.
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print("Part 1:", minimize_heat_loss(graph, start, end, part_2=False))
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print("Part 2:", minimize_heat_loss(graph, start, end, part_2=True))