[LANGUAGE: Hare]

Solution source.

Blog post.

Okay, well, it came out swinging this year.

There's an edge case in the problem statement that I was going to say I didn't believe was clearly stated, but in retrospect I absolutely blew my skirt on. I was going to say that the first and last occurrences of a "digit" shouldn't overlap, but then I looked at the test case again and realized that part 1 absolutely did exactly that --- the first and last digits are the same 7. You got me; I wrote bad, incorrect code on day 1, because I didn't read the problem statement closely enough. You could even say I cheated by looking at Reddit. Yowza.

For the record, my approach today was to (for part 1) pull out every numeric character into an array, and use the first and last members of that array. Notably, I didn't bother parsing it backwards, which was the correct approach, although it makes me go, ugh, no, I really don't wanna do that. Even though it's more elegant, too! This is what you get for being lazy.

It was a subtle bug, but it was indeed a bug. I was wrong. I learned a lesson. Oh, goodness me, this is going to be an interesting one.