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78 lines
2.2 KiB
Plaintext
78 lines
2.2 KiB
Plaintext
9 years ago
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#lang scribble/lp2
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@(require scribble/manual aoc-racket/helper)
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@aoc-title[5]
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Our @link-rp["day5-input.txt"]{input} is a list of random-looking but not really random text strings.
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@chunk[<day5>
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<day5-setup>
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<day5-q1>
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<day5-q2>
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<day5-test>]
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@section{How many strings are ``nice''?}
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A string is ``nice'' if it meets certain criteria:
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@itemlist[
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@item{Contains three vowels (= @litchar{aeiou}).}
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@item{Contains a double letter.}
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@item{Does not contain @litchar{ab}, @litchar{cd}, @litchar{pq}, or @litchar{xy}.}
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]
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This is a job for @racket[regexp-match]. There's nothing tricky here (except for remembering that certain matching functions require the @racket[pregexp] pattern prefix rather than @racket[regexp]).
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@chunk[<day5-setup>
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(require racket rackunit)
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]
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@chunk[<day5-q1>
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(define (nice? str)
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(define (three-vowels? str)
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(>= (length (regexp-match* #rx"[aeiou]" str)) 3))
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(define (double-letter? str)
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(regexp-match #px"(.)\\1" str))
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(define (no-kapu? str)
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(not (regexp-match #rx"ab|cd|pq|xy" str)))
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(and (three-vowels? str)
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(double-letter? str)
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(no-kapu? str)))
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(define (q1 words)
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(length (filter nice? words)))
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]
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@section{How many strings are ``nice'' under new rules?}
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This time a string is ``nice`` if it:
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@itemlist[
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@item{Contains a pair of two letters that appears twice without overlapping}
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@item{Contains a letter that repeats with at least one letter in between}
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]
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Again, a test of your regexp-writing skills.
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@chunk[<day5-q2>
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(define (nicer? str)
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(define (nonoverlapping-pair? str)
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(regexp-match #px"(..).*\\1" str))
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(define (separated-repeater? str)
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(regexp-match #px"(.).\\1" str))
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(and (nonoverlapping-pair? str)
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(separated-repeater? str) #t))
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(define (q2 words)
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(length (filter nicer? words)))]
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@section{Testing our input}
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@chunk[<day5-test>
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(module+ test
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(define input-str (file->lines "day5-input.txt"))
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(check-equal? (q1 input-str) 238)
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(check-equal? (q2 input-str) 69))]
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