2018-03-15 16:24:23 +00:00
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Advent of Code
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2016-12-16 22:21:15 +00:00
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2018-03-15 16:24:23 +00:00
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--- Day 20: Infinite Elves and Infinite Houses ---
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2016-12-16 22:21:15 +00:00
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2018-03-15 16:24:23 +00:00
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To keep the Elves busy, Santa has them deliver some presents by hand,
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door-to-door. He sends them down a street with infinite houses numbered
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sequentially: 1, 2, 3, 4, 5, and so on.
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2016-12-16 22:21:15 +00:00
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2018-03-15 16:24:23 +00:00
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Each Elf is assigned a number, too, and delivers presents to houses based on
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that number:
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2016-12-16 22:21:15 +00:00
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2018-03-15 16:24:23 +00:00
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• The first Elf (number 1) delivers presents to every house: 1, 2, 3, 4,
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5, ....
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2016-12-16 22:21:15 +00:00
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2018-03-15 16:24:23 +00:00
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• The second Elf (number 2) delivers presents to every second house: 2, 4,
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6, 8, 10, ....
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2016-12-16 22:21:15 +00:00
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2018-03-15 16:24:23 +00:00
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• Elf number 3 delivers presents to every third house: 3, 6, 9, 12, 15,
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....
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2016-12-16 22:21:15 +00:00
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2018-03-15 16:24:23 +00:00
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There are infinitely many Elves, numbered starting with 1. Each Elf delivers
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presents equal to ten times his or her number at each house.
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2016-12-16 22:21:15 +00:00
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So, the first nine houses on the street end up like this:
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House 1 got 10 presents.
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House 2 got 30 presents.
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House 3 got 40 presents.
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House 4 got 70 presents.
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House 5 got 60 presents.
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House 6 got 120 presents.
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House 7 got 80 presents.
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House 8 got 150 presents.
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House 9 got 130 presents.
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2018-03-15 16:24:23 +00:00
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The first house gets 10 presents: it is visited only by Elf 1, which
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delivers 1 * 10 = 10 presents. The fourth house gets 70 presents, because it
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is visited by Elves 1, 2, and 4, for a total of 10 + 20 + 40 = 70 presents.
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2016-12-16 22:21:15 +00:00
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2018-03-15 16:24:23 +00:00
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What is the lowest house number of the house to get at least as many
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presents as the number in your puzzle input?
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2016-12-16 22:21:15 +00:00
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Your puzzle answer was 831600.
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--- Part Two ---
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2018-03-15 16:24:23 +00:00
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The Elves decide they don't want to visit an infinite number of houses.
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Instead, each Elf will stop after delivering presents to 50 houses. To make
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up for it, they decide to deliver presents equal to eleven times their
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number at each house.
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2016-12-16 22:21:15 +00:00
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2018-03-15 16:24:23 +00:00
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With these changes, what is the new lowest house number of the house to get
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at least as many presents as the number in your puzzle input?
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2016-12-16 22:21:15 +00:00
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Your puzzle answer was 884520.
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Both parts of this puzzle are complete! They provide two gold stars: **
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2018-03-15 16:24:23 +00:00
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At this point, you should return to your advent calendar and try another
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puzzle.
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2016-12-16 22:21:15 +00:00
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Your puzzle input was 36000000.
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References
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Visible links
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. http://adventofcode.com/
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. http://adventofcode.com/about
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. http://adventofcode.com/stats
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. http://adventofcode.com/leaderboard
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. http://adventofcode.com/settings
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. http://adventofcode.com/auth/logout
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. http://adventofcode.com/
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