This is mostly from reusing the same object instead of creating a new one each time we test a new point, but there's also a minor amount of speedup from using HashSet instead of Dictionary. I originally thought I would need to care about why each spot was blocked (wall vs sand) but it turns out that's not important for this problem.
I am not completely happy with this data structure, but it's functional enough. I wanted to implement comparers and equality overrides for the classes to make part 2 shorter, but it would have come at the cost of a bunch of boilerplate code, so whatever.
This enables a flood-fill of distances from the goal location to every other location on the grid. With that, we only have to locate the node with the lowest distance value.
Technically this also solves part 1, but I wanted to leave the forward search in place as a test of sorts that the algorithm works both ways.
Now if I can just get the parse sped up...
This is quite slow, at least for part 2 (and part 1 is slower than I want it to be, event parse takes longer than I thought it should). I need a better approach to the second part. Probably need to mark all nodes' distances from the goal point instead of one-by-one plotting a path from each possible start to the end, but that requires an adjustment to how I'm building the graph in the first place.
This is ugly. I probably should've vec2'd this, made smarter move and follow logic that isn't a series of 'if's, and found a smarter way to calculate distance than my hackneyed vector distance, but it totally works so I'm rolling with it.
I'm sure there's a cleaner way to search in four directions rather than manually running each loop like this, but I didn't want to mess with genericizing it just yet.
A Deep Copy and a double-ended queue would have made this day much easier. I should add those. (Having trouble finding a generic deep copy that works in .net 6, though...I opted to rewrite my original List<List<char>> solution into List<string> in lieu of a deep copy so I wouldn't have to parse the input all over again.)
This is an ugly, kind-of-brute-force solution. I'm not proud of it, but it works and got me top 1000 on both parts.
I also changed the "which day to run if no day is specified" to just always choose the highest numbered day.
The 01a sample text file I created in VS2022 has a big-endian utf-16 byte order mark in front. When read with File.Read* methods it was fine, but when piped in from the command line it was causing the integer parsing to fail due to the extra bytes on the front. This is the cleanest way I can find to strip any of a set of BOMs from a string. Maybe there's an easier way somewhere, but the main issue is that using something like line[0..1].SequenceEqual() may or may not use wide chars (0xFEFF as opposed to 0xFE, 0xFF, for example) so I can't just build a list of preamble arrays and check if the byte version of the string starts with them.
The "StripPreamble" character list is still a mystery. I found it while working on my Macbook for aoc2021 and can't seem to find any search results indicating what these bytes represent, so...just gonna leave it there.
This enables the binary to be invoked from anywhere and still run on the default input set, as well as being more portable/shareable which can help with performance comparisons between machines. Files are still supported if they exist.
