src/2021/days/day-08.lisp @ 2848a4548adf
2023/01 and 2022/01
Also start porting my test data to the new account, since Twitter imploded and
apparently it's impossible for a website to store a goddamn username and
password in The Year of Our Lord 2023 so everyone just outsources auth all
the time, ugh.
author |
Steve Losh <steve@stevelosh.com> |
date |
Fri, 01 Dec 2023 11:05:43 -0500 |
parents |
0b68f84e44ae |
children |
(none) |
(advent:defpackage* :advent/2021/08
(:import-from :alexandria :length= :set-equal))
(in-package :advent/2021/08)
;; 0 . a b c e f g 6
;; 1 . c f 2
;; 2 . a c d e g 5
;; 3 . a c d f g 5
;; 4 . b c d f 4
;; 5 . a b d f g 5
;; 6 . a b d e f g 6
;; 7 . a c f 3
;; 8 . a b c d e f g 7
;; 9 . a b c d f g 6
(defun parse (stream)
(iterate
(for line :in-stream stream :using #'read-line)
(for words = (mapcar (rcurry #'coerce 'list) (str:split " " line)))
(collect (split-sequence:split-sequence '(#\|) words :test #'equal))))
(defun input (entry) (first entry))
(defun output (entry) (second entry))
(defun uniquep (word)
(member (length word) '(2 3 4 7)))
(defun supersetp (sup sub)
(and (subsetp sub sup)
(null (set-difference sub sup))))
(defun common-element (&rest sets)
(let ((result (reduce #'intersection sets)))
(assert (length= 1 result) () "No common element in ~S." sets)
(first result)))
(defun solve-entry (entry)
(let ((words (remove-duplicates (append (input entry) (output entry))
:test #'set-equal))
(solved (list))) ; alist of e.g. (1 . (#\a #\b))
(flet ((solve (n predicate)
(let ((result (find-if predicate words)))
(alexandria:deletef words result :test #'set-equal)
(push (cons n result) solved))))
;; * 1, 4, 7, 8 have unique lengths.
(solve 1 (curry #'length= 2))
(solve 4 (curry #'length= 4))
(solve 7 (curry #'length= 3))
(solve 8 (curry #'length= 7))
;; * 9 is a superset of 4.
(solve 9 (rcurry #'supersetp (assocdr 4 solved)))
;; * 0 is the 6-element superset of 7.
(solve 0 (lambda (word) (and (supersetp word (assocdr 7 solved)) (length= 6 word))))
;; * 3 is the 5-element superset of 7.
(solve 3 (lambda (word) (and (supersetp word (assocdr 7 solved)) (length= 5 word))))
;; * 6 is the only 6-element group left.
(solve 6 (curry #'length= 6))
;; * 5 contains the only element all the solved so far have in common.
(solve 5 (lambda (word)
(member (apply #'common-element (mapcar #'cdr solved))
word)))
;; * 2 is the last one left.
(solve 2 (constantly t))
;; Return the result.
(digits->number
(loop :for o :in (output entry)
:collect (rassocar o solved :test #'set-equal))))))
(defun part1 (entries)
(iterate (for entry :in entries)
(summing (count-if #'uniquep (output entry)))))
(defun part2 (entries)
(summation entries :key #'solve-entry))
(define-problem (2021 8) (data parse) (440 1046281)
(values (part1 data)
(part2 data)))
#; Scratch --------------------------------------------------------------------
(solve-entry
'(((#\a #\b #\c #\e #\f #\g)
(#\c #\f)
(#\a #\c #\d #\e #\g)
(#\a #\c #\d #\f #\g)
(#\b #\c #\d #\f)
(#\a #\b #\d #\f #\g)
(#\a #\b #\d #\e #\f #\g)
(#\a #\c #\f))
((#\a #\b #\c #\d #\e #\f #\g)
(#\a #\b #\c #\d #\f #\g))))