Day 21: Keypad Conundrum
Megathread guidelines
- Keep top level comments as only solutions, if you want to say something other than a solution put it in a new post. (replies to comments can be whatever)
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FAQ
- What is this?: Here is a post with a large amount of details: https://programming.dev/post/6637268
- Where do I participate?: https://adventofcode.com/
- Is there a leaderboard for the community?: We have a programming.dev leaderboard with the info on how to join in this post: https://programming.dev/post/6631465
Rust
For me this was the hardest puzzle so far this year. First I did a bunch of things that turned out not to work properly. For example I tried to solve it with a greedy algorithm that always moved horizontally first then vertically, but that ignores the gaps that need to be avoided (what a sneaky requirement) and also somehow doesn’t guarantee the shortest sequence.
After reaching part 2 it became clear that a recursive function (with memoization) is needed again, and of course in the end it turned out a lot simpler than what I had cooked up before (you don’t want to see that). Now even part 2 takes just 1.6ms.
Solution
Also on github
For a challenge that was conceptually very similar to Day 19, this one completely broke me all over again. I think it was just near impossible to mentally visualize. I only got it with lots of reading your code, so thanks!
I like your short cut of converting the keys from a grid to a set of coordinates, which really simplifies how you get the path.
Glad to be able to help. This one really was a doozy.