43 lines
1.3 KiB
EmacsLisp
43 lines
1.3 KiB
EmacsLisp
;; Advent of Code 2020 - Day 3
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(require 'cl-lib)
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(require 'dash)
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(require 'f)
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(require 's)
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(require 'seq)
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(setq day3/input
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(-filter (lambda (s) (not (seq-empty-p s)))
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(s-lines (f-read "/tmp/aoc/day3.txt"))))
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(setq day3/input-width (length (elt day3/input 0)))
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(setq day3/input-height (length day3/input))
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(defun day3/thing-at-point (x y)
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"Pun intentional."
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(when (>= day3/input-height y)
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(let ((x-repeated (mod (- x 1) day3/input-width)))
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(elt (elt day3/input (- y 1)) x-repeated))))
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(defun day3/slope (x-steps y-steps)
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"Produce the objects encountered through this slope until the
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bottom of the map."
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(cl-loop for x from 1 by x-steps
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for y from 1 to day3/input-height by y-steps
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collect (day3/thing-at-point x y)))
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;; Puzzle 1
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(defun day3/count-trees (x-steps y-steps)
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(cl-loop for thing being the elements of (day3/slope x-steps y-steps)
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count (= thing ?#)))
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(message "Solution to day3/1: One encounters %s trees" (day3/count-trees 3 1))
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;; Puzzle 2
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(message "Solution to day3/2 %s" (* (day3/count-trees 1 1)
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(day3/count-trees 3 1)
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(day3/count-trees 5 1)
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(day3/count-trees 7 1)
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(day3/count-trees 1 2)))
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