From 7db1c351c0b439dfc718fce60f34c5b40fb8dbbb Mon Sep 17 00:00:00 2001 From: "Timothy J. Warren" Date: Fri, 8 Dec 2023 12:12:36 -0500 Subject: [PATCH] Update readme --- 2023/day4/README.md | 44 ++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 44 insertions(+) diff --git a/2023/day4/README.md b/2023/day4/README.md index e375a05..4777283 100644 --- a/2023/day4/README.md +++ b/2023/day4/README.md @@ -54,3 +54,47 @@ the three matches after the first). So, in this example, the Elf's pile of scratchcards is worth `**13**` points. Take a seat in the large pile of colorful cards. **How many points are they worth in total?** + +# Part Two + +Just as you're about to report your findings to the Elf, one of you realizes that the rules have actually been printed +on the back of every card this whole time. + +There's no such thing as "points". Instead, scratchcards only cause you to win more scratchcards equal to the number +of winning numbers you have. + +Specifically, you win copies of the scratchcards below the winning card equal to the number of matches. So, if card +10 were to have 5 matching numbers, you would win one copy each of cards 11, 12, 13, 14, and 15. + +Copies of scratchcards are scored like normal scratchcards and have the same card number as the card they copied. So, +if you win a copy of card 10 and it has 5 matching numbers, it would then win a copy of the same cards that the +original card 10 won: cards 11, 12, 13, 14, and 15. This process repeats until none of the copies cause you to win +any more cards. (Cards will never make you copy a card past the end of the table.) + +This time, the above example goes differently: + +``` +Card 1: 41 48 83 86 17 | 83 86 6 31 17 9 48 53 +Card 2: 13 32 20 16 61 | 61 30 68 82 17 32 24 19 +Card 3: 1 21 53 59 44 | 69 82 63 72 16 21 14 1 +Card 4: 41 92 73 84 69 | 59 84 76 51 58 5 54 83 +Card 5: 87 83 26 28 32 | 88 30 70 12 93 22 82 36 +Card 6: 31 18 13 56 72 | 74 77 10 23 35 67 36 11 +``` + +- Card 1 has four matching numbers, so you win one copy each of the next four cards: cards 2, 3, 4, and 5. +- Your original card 2 has two matching numbers, so you win one copy each of cards 3 and 4. +- Your copy of card 2 also wins one copy each of cards 3 and 4. +- Your four instances of card 3 (one original and three copies) have two matching numbers, so you win four copies each of cards 4 and 5. +- Your eight instances of card 4 (one original and seven copies) have one matching number, so you win eight copies of card 5. +- Your fourteen instances of card 5 (one original and thirteen copies) have no matching numbers and win no more cards. +- Your one instance of card 6 (one original) has no matching numbers and wins no more cards. + +Once all of the originals and copies have been processed, you end up with 1 instance of card 1, 2 instances of card 2, +4 instances of card 3, 8 instances of card 4, 14 instances of card 5, and 1 instance of card 6. In total, this example +pile of scratchcards causes you to ultimately have 30 scratchcards! + +Process all of the original and copied scratchcards until no more scratchcards are won. Including the original set of +scratchcards, how many total scratchcards do you end up with? + +