Unfinished business

[softrabbit]

• Day 3, part 2.
• Day 8, part 2. The algorithm needs some more thought.
• Day 12, didn't really get anywhere when sitting down the first time. Doesn't look too bad, but... it's the graph implementing that's going to kill me.
• Day 14, part 2. Need to figure out a smart algorithm. The brute force one wants absurd amounts of memory, so a more efficient version of that would be interesting, too.