finish day4, reorg directory
parent
339b2c7d1d
commit
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#lang racket
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(require rackunit)
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(provide read-syntax)
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(define (get-dimensions str)
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(map string->number (regexp-match* #px"\\d+" str)))
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(define (get-faces dimensions)
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(define half-faces
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(for*/list ([first-pos (in-range (sub1 (length dimensions)))]
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[second-pos (in-range (add1 first-pos) (length dimensions))])
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(list (list-ref dimensions first-pos) (list-ref dimensions second-pos))))
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(append* (make-list 2 half-faces)))
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(define (str->paper str)
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(define dimensions (get-dimensions str))
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(define faces (get-faces dimensions))
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(define areas (map (curry apply *) faces))
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(define smallest-area (apply min areas))
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(apply + smallest-area areas))
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(define (str->ribbon str)
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(define dimensions (get-dimensions str))
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(define faces (get-faces dimensions))
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(define perimeters (map (λ(face) (* 2 (apply + face))) faces))
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(define smallest-perimeter (apply min perimeters))
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(define volume (apply * dimensions))
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(+ smallest-perimeter volume))
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(check-equal? (str->paper "2x3x4") 58)
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(check-equal? (str->paper "1x1x10") 43)
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(check-equal? (str->ribbon "2x3x4") 34)
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(check-equal? (str->ribbon "1x1x10") 14)
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(define (read-syntax source-path-string in-port)
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(with-syntax ([source-str (string-trim (port->string in-port))]
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[str->paper str->paper]
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[str->ribbon str->ribbon])
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#'(module _ racket
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(define package-strs (string-split 'source-str))
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(apply + (map str->paper package-strs))
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(apply + (map str->ribbon package-strs)))))
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@ -1,47 +0,0 @@
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#lang racket
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(require rackunit)
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(provide read-syntax)
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(define (str->visits str)
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(define start '(0 0))
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(define moves (map (λ(move) (case move
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[("^") '(0 1)]
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[("v") '(0 -1)]
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[("<") '(-1 0)]
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[(">") '(1 0)]))
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(regexp-match* #rx"." str)))
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(reverse (for/fold ([visit-acc (list start)])
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([move (in-list moves)])
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(cons (map + move (car visit-acc)) visit-acc))))
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(define (str->unique-visits str)
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(define visits (str->visits str))
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(length (remove-duplicates visits)))
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(define (str->robosanta str)
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(define-values (reversed-santa-path reversed-robo-path)
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(for/fold ([santa-acc empty][robo-acc empty])
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([c (in-string str)][pos (in-naturals)])
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(if (even? pos)
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(values (cons c santa-acc) robo-acc)
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(values santa-acc (cons c robo-acc)))))
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(define santa-str (string-append* (map ~a (reverse reversed-santa-path))))
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(define robo-str (string-append* (map ~a (reverse reversed-robo-path))))
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(length (remove-duplicates (append (str->visits santa-str) (str->visits robo-str)))))
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(check-equal? (str->unique-visits ">") 2)
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(check-equal? (str->unique-visits "^>v<") 4)
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(check-equal? (str->robosanta "^v") 3)
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(check-equal? (str->robosanta "^>v<") 3)
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(check-equal? (str->robosanta "^v^v^v^v^v") 11)
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(define (read-syntax source-path-string in-port)
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(with-syntax ([source-str (string-trim (port->string in-port))]
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[str->unique-visits str->unique-visits]
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[str->robosanta str->robosanta])
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#'(module _ racket
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(str->unique-visits source-str)
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(str->robosanta source-str))))
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@ -0,0 +1 @@
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iwrupvqb
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@ -0,0 +1,51 @@
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#lang scribble/lp2
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@(require scribble/manual aoc-racket/helper)
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@(require (for-label openssl/md5))
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@aoc-title[4]
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Our @link-rp["day4-input.txt"]{input} is a string of eight characters that represents part of a key for making an MD5 hash.
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@chunk[<day4>
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<setup>
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<q1>
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<q2>
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<test>]
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@section{What is the lowest-numbered MD5 hash starting with five zeroes?}
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We're asked to create an MD5 hash from an input key that consists of our eight-character input joined to a decimal number. The puzzle asks us to find the lowest decimal number that, when joined to our input, produces an MD5 hash that starts with five zeroes.
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Whether or not you already know what an MD5 hash is, you can search the Racket docs and will soon find the @racketmodname[openssl/md5] module and the @racket[md5] function. Then, this puzzle is easy: starting at @racket[0], make new input keys with each integer, and stop when we find one that results in the MD5 hash we want. (The approach is similar to the second part of @secref["day-1"].)
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@chunk[<setup>
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(require racket rackunit openssl/md5)
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]
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@chunk[<q1>
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(define (q1 str)
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(for/or ([i (in-naturals)])
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(define md5-key (string-append str (~a i)))
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(define md5-hash (md5 (open-input-string md5-key)))
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(and (string-prefix? md5-hash "00000") i)))
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]
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@section{How about six zeroes?}
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Exactly the same, except we test for a string of six zeroes. It is likely, however, to take quite a bit longer to run, as the sixth zero essentially makes the criterion 10 times more stringent.
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@chunk[<q2>
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(define (q2 str)
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(for/or ([i (in-naturals)])
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(define md5-key (string-append str (~a i)))
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(define md5-hash (md5 (open-input-string md5-key)))
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(and (string-prefix? md5-hash "000000") i)))]
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@section{Testing our input}
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@chunk[<test>
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(module+ test
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(define input-str (file->string "day4-input.txt"))
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(check-equal? (q1 input-str) 346386)
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(check-equal? (q2 input-str) 9958218))]
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