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authorBryan Brattlof <hello@bryanbrattlof.com>2020-12-11 12:34:23 -0500
committerBryan Brattlof <hello@bryanbrattlof.com>2020-12-11 12:34:23 -0500
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day03: add first question
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+Day 3: Toboggan Trajectory
+##########################
+
+With the toboggan login problems resolved, you set off toward the airport. While
+travel by toboggan might be easy, it's certainly not safe: there's very minimal
+steering and the area is covered in trees. You'll need to see which angles will
+take you near the fewest trees.
+
+Due to the local geology, trees in this area only grow on exact integer
+coordinates in a grid. You make a map (your puzzle input) of the open squares
+(.) and trees (#) you can see. For example:
+
+.. code-block::
+
+ ..##.......
+ #...#...#..
+ .#....#..#.
+ ..#.#...#.#
+ .#...##..#.
+ ..#.##.....
+ .#.#.#....#
+ .#........#
+ #.##...#...
+ #...##....#
+ .#..#...#.#
+
+These aren't the only trees, though; due to something you read about once
+involving arboreal genetics and biome stability, the same pattern repeats to the
+right many times:
+
+.. code-block::
+
+ ..##.........##.........##.........##.........##.........##....... --->
+ #...#...#..#...#...#..#...#...#..#...#...#..#...#...#..#...#...#..
+ .#....#..#..#....#..#..#....#..#..#....#..#..#....#..#..#....#..#.
+ ..#.#...#.#..#.#...#.#..#.#...#.#..#.#...#.#..#.#...#.#..#.#...#.#
+ .#...##..#..#...##..#..#...##..#..#...##..#..#...##..#..#...##..#.
+ ..#.##.......#.##.......#.##.......#.##.......#.##.......#.##..... --->
+ .#.#.#....#.#.#.#....#.#.#.#....#.#.#.#....#.#.#.#....#.#.#.#....#
+ .#........#.#........#.#........#.#........#.#........#.#........#
+ #.##...#...#.##...#...#.##...#...#.##...#...#.##...#...#.##...#...
+ #...##....##...##....##...##....##...##....##...##....##...##....#
+ .#..#...#.#.#..#...#.#.#..#...#.#.#..#...#.#.#..#...#.#.#..#...#.# --->
+
+You start on the open square (.) in the top-left corner and need to reach the
+bottom (below the bottom-most row on your map).
+
+The toboggan can only follow a few specific slopes (you opted for a cheaper
+model that prefers rational numbers); start by counting all the trees you would
+encounter for the slope right 3, down 1:
+
+From your starting position at the top-left, check the position that is right 3
+and down 1. Then, check the position that is right 3 and down 1 from there, and
+so on until you go past the bottom of the map.
+
+The locations you'd check in the above example are marked here with O where
+there was an open square and X where there was a tree:
+
+.. code-block:: terminal
+
+ ..##.........##.........##.........##.........##.........##....... --->
+ #..O#...#..#...#...#..#...#...#..#...#...#..#...#...#..#...#...#..
+ .#....X..#..#....#..#..#....#..#..#....#..#..#....#..#..#....#..#.
+ ..#.#...#O#..#.#...#.#..#.#...#.#..#.#...#.#..#.#...#.#..#.#...#.#
+ .#...##..#..X...##..#..#...##..#..#...##..#..#...##..#..#...##..#.
+ ..#.##.......#.X#.......#.##.......#.##.......#.##.......#.##..... --->
+ .#.#.#....#.#.#.#.O..#.#.#.#....#.#.#.#....#.#.#.#....#.#.#.#....#
+ .#........#.#........X.#........#.#........#.#........#.#........#
+ #.##...#...#.##...#...#.X#...#...#.##...#...#.##...#...#.##...#...
+ #...##....##...##....##...#X....##...##....##...##....##...##....#
+ .#..#...#.#.#..#...#.#.#..#...X.#.#..#...#.#.#..#...#.#.#..#...#.# --->
+
+In this example, traversing the map using this slope would cause you to
+encounter 7 trees.
+
+Starting at the top-left corner of your map and following a slope of right 3 and
+down 1, how many trees would you encounter?