Stream: advent of code

Topic: Day 9

Kevin Gillette (Dec 09 2022 at 08:26):

If you get stuck on day 9, carefully reread the movement instructions:

If the head is ever two steps directly up, down, left, or right from the tail, the tail must also move one step in that direction so it remains close enough.
Otherwise, if the head and tail aren't touching and aren't in the same row or column, the tail always moves one step diagonally to keep up.

I had mis-inferred that the tail knot should merely go where the head knot had previously been whenever they're too far away. That turns out to be entirely equivalent in effect to ^^ for part 1, but doesn't work at all for part 2. I find it hard to locate (or even notice) instructions in diagram-heavy puzzle days like this one, so spent about 90 minutes just trying random stuff before carefully rereading.

Shritesh Bhattarai (Dec 09 2022 at 15:49):

Here's my day 9. I'm sure I would have given up between part 1 and 2 if I didn't have a type system to guide me through the refactoring.

Luke Boswell (Dec 10 2022 at 06:24):

Here is my Day 9 solution. I really enjoyed this one. :smiley:

Ayaz Hafiz (Dec 11 2022 at 22:21):

My day 9. I also thought this was a fun one

Last updated: Jul 26 2025 at 12:14 UTC