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