120 lines
4.9 KiB
Plaintext
120 lines
4.9 KiB
Plaintext
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# Advent of Code
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--- Day 3: Toboggan Trajectory ---
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With the toboggan login problems resolved, you set off toward the airport. While travel by
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toboggan might be easy, it's certainly not safe: there's very minimal steering and the area
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is covered in trees. You'll need to see which angles will take you near the fewest trees.
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Due to the local geology, trees in this area only grow on exact integer coordinates in a
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grid. You make a map (your puzzle input) of the open squares (.) and trees (#) you can see.
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For example:
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..##.......
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#...#...#..
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.#....#..#.
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..#.#...#.#
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.#...##..#.
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..#.##.....
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.#.#.#....#
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.#........#
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#.##...#...
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#...##....#
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.#..#...#.#
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These aren't the only trees, though; due to something you read about once involving
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arboreal genetics and biome stability, the same pattern repeats to the right many times:
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..##.........##.........##.........##.........##.........##....... --->
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#...#...#..#...#...#..#...#...#..#...#...#..#...#...#..#...#...#..
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.#....#..#..#....#..#..#....#..#..#....#..#..#....#..#..#....#..#.
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..#.#...#.#..#.#...#.#..#.#...#.#..#.#...#.#..#.#...#.#..#.#...#.#
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.#...##..#..#...##..#..#...##..#..#...##..#..#...##..#..#...##..#.
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..#.##.......#.##.......#.##.......#.##.......#.##.......#.##..... --->
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.#.#.#....#.#.#.#....#.#.#.#....#.#.#.#....#.#.#.#....#.#.#.#....#
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.#........#.#........#.#........#.#........#.#........#.#........#
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#.##...#...#.##...#...#.##...#...#.##...#...#.##...#...#.##...#...
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#...##....##...##....##...##....##...##....##...##....##...##....#
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.#..#...#.#.#..#...#.#.#..#...#.#.#..#...#.#.#..#...#.#.#..#...#.# --->
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You start on the open square (.) in the top-left corner and need to reach the bottom (below
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the bottom-most row on your map).
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The toboggan can only follow a few specific slopes (you opted for a cheaper model that
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prefers rational numbers); start by counting all the trees you would encounter for the
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slope right 3, down 1:
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From your starting position at the top-left, check the position that is right 3 and down 1.
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Then, check the position that is right 3 and down 1 from there, and so on until you go past
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the bottom of the map.
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The locations you'd check in the above example are marked here with O where there was an
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open square and X where there was a tree:
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..##.........##.........##.........##.........##.........##....... --->
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#..O#...#..#...#...#..#...#...#..#...#...#..#...#...#..#...#...#..
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.#....X..#..#....#..#..#....#..#..#....#..#..#....#..#..#....#..#.
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..#.#...#O#..#.#...#.#..#.#...#.#..#.#...#.#..#.#...#.#..#.#...#.#
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.#...##..#..X...##..#..#...##..#..#...##..#..#...##..#..#...##..#.
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..#.##.......#.X#.......#.##.......#.##.......#.##.......#.##..... --->
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.#.#.#....#.#.#.#.O..#.#.#.#....#.#.#.#....#.#.#.#....#.#.#.#....#
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.#........#.#........X.#........#.#........#.#........#.#........#
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#.##...#...#.##...#...#.X#...#...#.##...#...#.##...#...#.##...#...
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#...##....##...##....##...#X....##...##....##...##....##...##....#
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.#..#...#.#.#..#...#.#.#..#...X.#.#..#...#.#.#..#...#.#.#..#...#.# --->
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In this example, traversing the map using this slope would cause you to encounter 7 trees.
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Starting at the top-left corner of your map and following a slope of right 3 and down 1,
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how many trees would you encounter?
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Your puzzle answer was 289.
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--- Part Two ---
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Time to check the rest of the slopes - you need to minimize the probability of a sudden
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arboreal stop, after all.
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Determine the number of trees you would encounter if, for each of the following slopes, you
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start at the top-left corner and traverse the map all the way to the bottom:
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• Right 1, down 1.
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• Right 3, down 1. (This is the slope you already checked.)
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• Right 5, down 1.
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• Right 7, down 1.
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• Right 1, down 2.
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In the above example, these slopes would find 2, 7, 3, 4, and 2 tree(s) respectively;
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multiplied together, these produce the answer 336.
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What do you get if you multiply together the number of trees encountered on each of the
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listed slopes?
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Your puzzle answer was 5522401584.
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Both parts of this puzzle are complete! They provide two gold stars: **
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At this point, you should return to your Advent calendar and try another puzzle.
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If you still want to see it, you can get your puzzle input.
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References
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Visible links
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. https://adventofcode.com/
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. https://adventofcode.com/2020/about
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. https://adventofcode.com/2020/events
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. https://adventofcode.com/2020/settings
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. https://adventofcode.com/2020/auth/logout
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. Advent of Code Supporter
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https://adventofcode.com/2020/support
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. https://adventofcode.com/2020
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. https://adventofcode.com/2020
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. https://adventofcode.com/2020/support
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. https://adventofcode.com/2020/sponsors
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. https://adventofcode.com/2020/leaderboard
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. https://adventofcode.com/2020/stats
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. https://adventofcode.com/2020/sponsors
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. https://adventofcode.com/2020
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. https://adventofcode.com/2020/day/3/input
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