Day 3

03-tobogganTrajectory/README.md

@@ -0,0 +1,101 @@
+# Day 3: Toboggan Trajectory
+
+<details><summary>Challenge description</summary>
+
+## Part One
+
+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?
+
+Your puzzle answer was `292`.
+
+## Part Two
+
+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?
+
+Your puzzle answer was `9354744432`.
+
+</details>
+
+<details><summary>Script output</summary>
+
+```
+❯ python .\main.py
+Pair (3, 1): 292 trees (part one solution)
+Pair (1, 1): 81 trees
+Pair (5, 1): 89 trees
+Pair (7, 1): 101 trees
+Pair (1, 2): 44 trees
+Product of all: 9354744432 (part two solution)
+```
+
+</details>

03-tobogganTrajectory/input.txt

@@ -0,0 +1,323 @@
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03-tobogganTrajectory/main.py

@@ -0,0 +1,34 @@
+input_list = open("input.txt").read().strip().split("\n")
+
+forest = [[char for char in line] for line in input_list]
+
+tree_char = "#"
+
+def find_collisions(forest:list, x_offset:int, y_offset:int) -> int:
+    encountered_trees = 0
+    x_pointer = 0
+
+    for row in forest[::y_offset]:
+        target_index = x_pointer % len(row)
+        if row[target_index] == tree_char:
+            encountered_trees += 1
+        x_pointer += x_offset
+
+    return encountered_trees
+
+offset_pairs = [
+    (3, 1),
+    (1, 1),
+    (5, 1),
+    (7, 1),
+    (1, 2)
+]
+
+tree_product = 1
+
+for i, pair in enumerate(offset_pairs):
+    encountered_trees = find_collisions(forest, *pair)
+    tree_product *= encountered_trees
+    print(f"Pair {pair}: {encountered_trees} trees", ("(part one solution)" if i == 0 else ""))
+
+print(f"Product of all: {tree_product} (part two solution)")