2020 Day 03, unified headers for 2020

2020/03/README.md

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+# 2020 Day 3: Toboggan Trajectory  
+Copyright (c) Eric Wastl
+#### [Direct Link](https://adventofcode.com/2020/day/3)
+
+## Part 1
+
+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:
+
+```
+..##.......
+#...#...#..
+.#....#..#.
+..#.#...#.#
+.#...##..#.
+..#.##.....
+.#.#.#....#
+.#........#
+#.##...#...
+#...##....#
+.#..#...#.#
+```
+
+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:
+
+```
+..##.........##.........##.........##.........##.........##.......  --->
+#...#...#..#...#...#..#...#...#..#...#...#..#...#...#..#...#...#..
+.#....#..#..#....#..#..#....#..#..#....#..#..#....#..#..#....#..#.
+..#.#...#.#..#.#...#.#..#.#...#.#..#.#...#.#..#.#...#.#..#.#...#.#
+.#...##..#..#...##..#..#...##..#..#...##..#..#...##..#..#...##..#.
+..#.##.......#.##.......#.##.......#.##.......#.##.......#.##.....  --->
+.#.#.#....#.#.#.#....#.#.#.#....#.#.#.#....#.#.#.#....#.#.#.#....#
+.#........#.#........#.#........#.#........#.#........#.#........#
+#.##...#...#.##...#...#.##...#...#.##...#...#.##...#...#.##...#...
+#...##....##...##....##...##....##...##....##...##....##...##....#
+.#..#...#.#.#..#...#.#.#..#...#.#.#..#...#.#.#..#...#.#.#..#...#.#  --->
+```
+
+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:
+
+```
+..##.........##.........##.........##.........##.........##.......  --->
+#..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?**
+
+## Part 2
+
+Time to check the rest of the slopes - you need to minimize the probability of a sudden arboreal stop, after all.
+
+Determine the number of trees you would encounter if, for each of the following slopes, you start at the top-left corner and traverse the map all the way to the bottom:
+
+- Right 1, down 1.
+- Right 3, down 1. (This is the slope you already checked.)
+- Right 5, down 1.
+- Right 7, down 1.
+- Right 1, down 2.
+
+In the above example, these slopes would find `2`, `7`, `3`, `4`, and `2` tree(s) respectively; multiplied together, these produce the answer **`336`**.
+
+**What do you get if you multiply together the number of trees encountered on each of the listed slopes?**