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#lang reader "../aoc-lang.rkt"
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(require racket/sequence sugar/list)
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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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(time ((if (eq? 'STARS '★) one-star two-star) (format "~a" 'STR))) ...))
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(define (knot-hashes str)
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(for/list ([i (in-range 128)])
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(knot-hash (format "~a-~a" str i))))
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(define (one-star str)
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(for*/sum ([kh (in-list (knot-hashes str))]
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[int (in-list (kh->ints kh))])
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int))
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(define (two-star str)
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(define vec (for*/vector ([kh (in-list (knot-hashes str))]
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[int (in-list (kh->ints kh))])
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(if (= int 1) 'used 'empty)))
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(define (at-left-edge? idx) (= (modulo idx 128) 0))
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(define (at-right-edge? idx) (= (modulo idx 128) 127))
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(for/fold ([region 0])
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([(val idx) (in-indexed vec)]
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#:unless (number? val))
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(let loop ([idx idx])
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(cond
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[(and (<= 0 idx (sub1 (vector-length vec))) (eq? (vector-ref vec idx) 'used))
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(vector-set! vec idx region)
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(unless (at-left-edge? idx) (loop (sub1 idx)))
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(unless (at-right-edge? idx) (loop (add1 idx)))
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(loop (+ idx 128))
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(loop (- idx 128))
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(add1 region)]
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[else region]))))
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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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(if (char=? c #\1) 1 0)))
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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 (λ (posn) (vector-ref vec posn)) 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)) |