I did a different heuristic for A*: I ran a Dijkstra backwards from the bottom right corner and computed the heat losses for each block if there were no movement restrictions whatsoever. Maybe that'll help shave more milliseconds :)
this post was submitted on 17 Dec 2023
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Advent Of Code
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Interesting! I'll try that out!
Clever! And removing constraints doesn't increase the path cost, so it won't be an overestimate.
Some (not very insightful or helpful) observations:
- The shortest path is likely to be mostly monotonic (it's quite hard for the "long way round" to be cost-effective), so the Manhattan distance is probably a good metric.
- The center of the puzzle is expensive, so the straight-line distance is probably not a good metric
- I'm pretty sure that the shortest route (for part one at least) can't self-intersect. Implementing this constraint is probably not going to speed things up, and there might be some pathological case where it's not true.
Not an optimization, but I suspect that a heuristic-based "reasonably good" path such as a human would take will be fairly close to optimal.