| 1 | (in-package #:adventofcode2020) |
| 2 | |
| 3 | (defun tree-collisions (slope tree-map) |
| 4 | (destructuring-bind (rise run) slope |
| 5 | (loop with terrain-width = (-> tree-map first length) |
| 6 | for i upfrom 0 by run |
| 7 | for j upfrom 0 |
| 8 | for terrain-line in tree-map |
| 9 | when (->> rise (mod j) (= 0)) |
| 10 | counting (->> terrain-width |
| 11 | (mod i) |
| 12 | (char terrain-line) |
| 13 | (char= #\#))))) |
| 14 | |
| 15 | (day 03 input |
| 16 | (let ((tree-map (list-from input))) |
| 17 | (part1 (tree-collisions '(1 3) tree-map)) |
| 18 | (part2 (->> '((1 1) (1 3) (1 5) (1 7) (2 1)) |
| 19 | (mapcar (fn* (tree-collisions _ tree-map))) |
| 20 | (reduce #'*))))) |
| 21 | |
| 22 | (def-suite day03) |
| 23 | (in-suite day03) |
| 24 | |
| 25 | (test single-collision-check |
| 26 | (is (equal |
| 27 | 7 |
| 28 | (tree-collisions '(1 3) '("..##......." |
| 29 | "#...#...#.." |
| 30 | ".#....#..#." |
| 31 | "..#.#...#.#" |
| 32 | ".#...##..#." |
| 33 | "..#.##....." |
| 34 | ".#.#.#....#" |
| 35 | ".#........#" |
| 36 | "#.##...#..." |
| 37 | "#...##....#" |
| 38 | ".#..#...#.#"))))) |
| 39 | |
| 40 | |
| 41 | (test multiple-collision-check |
| 42 | (is (equal |
| 43 | '(2 7 3 4 2) |
| 44 | (mapcar (fn* (tree-collisions _ '("..##......." |
| 45 | "#...#...#.." |
| 46 | ".#....#..#." |
| 47 | "..#.#...#.#" |
| 48 | ".#...##..#." |
| 49 | "..#.##....." |
| 50 | ".#.#.#....#" |
| 51 | ".#........#" |
| 52 | "#.##...#..." |
| 53 | "#...##....#" |
| 54 | ".#..#...#.#"))) |
| 55 | '((1 1) (1 3) (1 5) (1 7) (2 1)))))) |
| 56 | |
| 57 | (run! 'day03) |