Thanks for putting this together--this brought me a lot of joy this year! I only got Day 15 wrong and I really don't understand why, but was still able to solve it all, which was very satisfying.
PS, I am sure there is an elegant way to do #21, but I also just did it brutishly in Excel.
@Chad: What was your wrong answer for #15? I had that one wrong too at first, and it took a kind of sneaky "Oh of course!" insight for me to figure it out.
PS, I am sure there is an elegant way to do #21, but I also just did it brutishly in Excel.
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