src/day05.lisp

   1 (asdf:load-system :adventofcode2020)
   2 (in-package #:adventofcode2020)
   3
   4 (defun calc-seat (seat-spec)
   5   (loop with len = (1- (length seat-spec))
   6         for c across seat-spec
   7         for i downfrom len
   8         summing (if (or (char= c #\R) (char= c #\B))
   9                     (ash 1 i) 0)))
  10
  11 (day 05 input
  12   (let* ((lines (list-from input))
  13          (seat-ids (-<>> lines
  14                      (mapcar #'calc-seat)
  15                      (sort <> #'>))))
  16     (part1 (first seat-ids))
  17     (part2 (loop for big in seat-ids
  18                  for small in (cdr seat-ids)
  19                  when (= small (- big 2))
  20                  return (1+ small)))))
  21
  22 (def-suite day05)
  23 (in-suite day05)
  24
  25 (test calc-seats
  26   (is (equal
  27         '(357 567 119 820)
  28         (mapcar #'calc-seat '("FBFBBFFRLR" "BFFFBBFRRR"
  29                               "FFFBBBFRRR" "BBFFBBFRLL")))))
  30
  31 (run! 'day05)