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64 lines
2.5 KiB
Racket
64 lines
2.5 KiB
Racket
#lang br
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(require racket/file rackunit csp racket/set racket/dict)
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(match-define (list fields my-ticket other-tickets)
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(string-split (file->string "16.rktd") "\n\n"))
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(struct predicate (name func) #:transparent)
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(define predicates
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(for/list ([field (string-split fields "\n")])
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(match (regexp-match #px"^(.*?): (\\d+)-(\\d+) or (\\d+)-(\\d+)$" field)
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[(list* _ name numstrs)
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(match-define (list val1 val2 val3 val4) (map string->number numstrs))
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(predicate name (λ (x)
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(let ([h (make-hasheq)])
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(hash-ref! h x
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(λ ()
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(or (<= val1 x val2) (<= val3 x val4)))))))])))
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(define (ticket->ints t) (map string->number (string-split t ",")))
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(check-equal? (for*/sum ([ticket (cdr (string-split other-tickets "\n"))]
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[ticket-int (ticket->ints ticket)]
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#:unless (for/or ([pred predicates])
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((predicate-func pred) ticket-int)))
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ticket-int) 26988)
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(define all-tickets (cdr (string-split other-tickets "\n")))
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(define (ticket-valid? ticket)
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(for/and ([intvec (ticket->ints ticket)])
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(for/or ([pred predicates])
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((predicate-func pred) intvec))))
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(define valid-tickets (filter ticket-valid? all-tickets))
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(define cols (apply map list (map ticket->ints valid-tickets)))
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(define col-preds (make-hasheq))
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(for ([(col colidx) (in-indexed cols)])
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(hash-set! col-preds colidx
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(apply mutable-set (for/list ([(pred predidx) (in-indexed predicates)]
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#:when (andmap (predicate-func pred) col))
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predidx))))
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(define assignment (make-hasheq))
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(let loop ()
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(define unique-pairs (for/list ([(colidx predidx) (in-dict (hash->list col-preds))]
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#:when (eq? (set-count predidx) 1))
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(cons colidx (car (set->list predidx)))))
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(when (pair? unique-pairs)
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(for ([(colidx predidx) (in-dict unique-pairs)])
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(hash-set! assignment colidx predidx)
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(hash-remove! col-preds colidx)
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(for ([k (in-hash-keys col-preds)])
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(hash-update! col-preds k (λ (vs) (set-remove! vs predidx) vs))))
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(loop)))
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(check-equal?
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(for*/product ([(colidx predidx) (in-hash assignment)]
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[pred (in-value (list-ref predicates predidx))]
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#:when (regexp-match "departure" (predicate-name pred)))
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(list-ref (ticket->ints my-ticket) colidx))
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426362917709) |