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feat(tazjin/aoc2020): Add solution for day 3

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Change-Id: I84147731e1508032510a52cda28be74bbbb17c61
Reviewed-on: https://cl.tvl.fyi/c/depot/+/2225
Reviewed-by: tazjin <mail@tazj.in>
Tested-by: BuildkiteCI
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Vincent Ambo 2020-12-04 10:59:57 +01:00 committed by tazjin
parent ea683b1ce8
commit a9980bb631
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;; Advent of Code 2020 - Day 3
(require 'cl-lib)
(require 'dash)
(require 'f)
(require 's)
(require 'seq)
(setq day3/input
(-filter (lambda (s) (not (seq-empty-p s)))
(s-lines (f-read "/tmp/aoc/day3.txt"))))
(setq day3/input-width (length (elt day3/input 0)))
(setq day3/input-height (length day3/input))
(defun day3/thing-at-point (x y)
"Pun intentional."
(when (>= day3/input-height y)
(let ((x-repeated (mod (- x 1) day3/input-width)))
(elt (elt day3/input (- y 1)) x-repeated))))
(defun day3/slope (x-steps y-steps)
"Produce the objects encountered through this slope until the
bottom of the map."
(cl-loop for x from 1 by x-steps
for y from 1 to day3/input-height by y-steps
collect (day3/thing-at-point x y)))
;; Puzzle 1
(defun day3/count-trees (x-steps y-steps)
(cl-loop for thing being the elements of (day3/slope x-steps y-steps)
count (= thing ?#)))
(message "Solution to day3/1: One encounters %s trees" (day3/count-trees 3 1))
;; Puzzle 2
(message "Solution to day3/2 %s" (* (day3/count-trees 1 1)
(day3/count-trees 3 1)
(day3/count-trees 5 1)
(day3/count-trees 7 1)
(day3/count-trees 1 2)))