Solution to problem 3 in Python

src/P3.py

@@ -0,0 +1,89 @@
+# --- 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:
+
+# ..##.......
+# #...#...#..
+# .#....#..#.
+# ..#.#...#.#
+# .#...##..#.
+# ..#.##.....
+# .#.#.#....#
+# .#........#
+# #.##...#...
+# #...##....#
+# .#..#...#.#
+
+# 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?
+
+
+with open("files/P3.txt", "r") as f:
+    forest = [line.split() for line in f.read().strip().split("\n")]
+
+
+def part_1() -> None:
+    trees_found, pos = 0, 0
+    for idx, line in enumerate(forest):
+        extended_line = ",".join(line * 32).replace(",", "")
+        if extended_line[pos] == "#":
+            trees_found += 1
+        pos += 3
+
+    print(f"We found {trees_found} trees in our way")
+
+
+if __name__ == "__main__":
+    part_1()