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40 lines
1.6 KiB
Racket
40 lines
1.6 KiB
Racket
#lang reader "../aoc-lang.rkt"
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(require racket/sequence)
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(provide (rename-out [#%mb #%module-begin]))
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(define-macro (#%mb (STARS) (STR) ...)
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#`(#%module-begin
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((if (eq? 'STARS '★) one-star (λ (x) #f)) (format "~a" 'STR)) ...))
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(define (one-star str)
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(for*/sum ([i (in-range 128)]
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[digit (in-list (kh->ints (knot-hash (format "~a-~a" str i))))])
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digit))
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(define (kh->ints kh)
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(for*/list ([c (in-string kh)]
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[num (in-value (string->number (string c) 16))]
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[c (in-string (~r num #:base 2 #:min-width 4 #:pad-string "0"))])
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(string->number (string c))))
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(define (knot-hash seed-str [range-in 256])
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(define ascii-chars (map char->integer (string->list seed-str)))
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(define nums (reverse-segments range-in (append ascii-chars '(17 31 73 47 23)) #:reps 64))
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(define dense-hash (for/list ([vals (in-slice 16 nums)])
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(apply bitwise-xor vals)))
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(string-append* (for/list ([num (in-list dense-hash)])
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(~r num #:base 16 #:min-width 2 #:pad-string "0"))))
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(define (reverse-segments range-in lens #:reps [reps 1])
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(define vec (list->vector (range range-in)))
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(for*/fold ([current-position 0]
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[skip-size 0])
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([rep (in-range reps)]
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[len (in-list lens)])
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(define posns (for/list ([i (in-range len)])
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(modulo (+ current-position i) range-in)))
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(for ([val (in-list (map (curry vector-ref vec) posns))]
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[posn (in-list (reverse posns))])
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(vector-set! vec posn val))
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(values (+ current-position len skip-size) (add1 skip-size)))
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(vector->list vec)) |