My Advent of Code solutions in Python.
kevinyap.ca/2019/12/going-fast-in-advent-of-code/
advent-of-code
python
Update solution for 2023/17
Represent state as the most recent direction moved and the number of
times we have moved in that direction sequentially, since that's the
only information that is actually relevant (essentially adding a 3rd
dimension to the traversal where we move down the Z-axis while moving
in the same direction and then pop up to layer z=0 when turning.)
+17
-20
+15
-20
2023/day17.py
+15
-20
2023/day17.py
···
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1
import fileinput
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2
import heapq
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-
from utils import Point, DIRS, N, S, E, W
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+
from utils import Point, DIRS
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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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+
def gen_neighbours(node, last_dir, last_count):
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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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+
if last_dir is not None:
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# No U-turns allowed.
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if hist[-1] == -d:
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if last_dir == -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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-
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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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if last_count < 4 and d != last_dir:
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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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if last_count == 10 and d == last_dir:
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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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+
if last_count == 3 and last_dir == d:
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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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+
horizon = [(0, start, None, 0)]
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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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depth, curr, last_dir, last_count = heapq.heappop(horizon)
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if (curr, hist) in seen:
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if (curr, last_dir, last_count) in seen:
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continue
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seen.add((curr, hist))
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seen.add((curr, last_dir, last_count))
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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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if curr == goal and (not part_2 or last_count >= 4):
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return depth
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for neighbour, weight, nd in gen_neighbours(curr, hist):
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for neighbour, weight, nd in gen_neighbours(curr, last_dir, last_count):
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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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new_count = 1 if nd != last_dir else last_count + 1
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heapq.heappush(horizon, (new_cost, neighbour, nd, new_count))
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# Read problem input.