src/day05.lisp

   1 (asdf:load-system :adventofcode2020)
   2 (in-package #:adventofcode2020)
   3
   4 (defun calc-seat (seat-spec)
   5   (let ((row (string-right-trim "RL" seat-spec))
   6          (col (string-left-trim "FB" seat-spec))
   7          (convert-to-int
   8            (lambda (str one)
   9              (loop with len = (1- (length str))
  10                    for c across str
  11                    for i downfrom len
  12                    summing (if (char= c one)
  13                                (ash 1 i) 0)))))
  14      (mapcar convert-to-int (list row col) '(#\B #\R))))
  15
  16 (defun calc-seat-id (row-col)
  17   (destructuring-bind (row col) row-col
  18     (+ (* row 8) col)))
  19
  20 (day 05 input
  21   (let* ((lines (list-from input))
  22          (seat-ids (-<>> lines
  23                      (mapcar (compose #'calc-seat-id #'calc-seat))
  24                      (sort <> #'>))))
  25     (part1 (first seat-ids))
  26     (part2 (loop for big in seat-ids
  27                  for small in (cdr seat-ids)
  28                  when (= small (- big 2))
  29                  return (1+ small)))))
  30
  31 (def-suite day05)
  32 (in-suite day05)
  33
  34 (test calc-seats
  35   (is (equal
  36         '((44 5) (70 7) (14 7) (102 4))
  37         (mapcar #'calc-seat '("FBFBBFFRLR" "BFFFBBFRRR"
  38                               "FFFBBBFRRR" "BBFFBBFRLL")))))
  39
  40 (run! 'day05)