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#lang br
(require racket/file rackunit)
(define lines (map string->list (file->lines "10.rktd")))
(define left-toks (list #\[ #\( #\{ #\<))
(define right-toks (list #\] #\) #\} #\>))
(define duos (map list left-toks right-toks))
(define (matched-pair? left right) (member (list left right) duos))
(define (parse tokens)
(with-handlers ([char? values])
(let loop ([tokens tokens][lefts null])
[(empty? tokens) lefts]
[(memv (car tokens) left-toks)
(loop (cdr tokens) (cons (car tokens) lefts))]
[(and (pair? lefts) (matched-pair? (car lefts) (car tokens)))
(loop (cdr tokens) (cdr lefts))]
[else (raise (car tokens))]))))
(define (corrupt? parsed-line)
(case parsed-line
[(#\)) 3]
[(#\]) 57]
[(#\}) 1197]
[(#\>) 25137]
[else #f]))
(check-equal? (apply + (filter-map corrupt? (map parse lines))) 366027)
(define (autocomplete-score parsed-line)
(for/fold ([total 0])
([c parsed-line])
(+ (* total 5) (case c
[(#\() 1]
[(#\[) 2]
[(#\{) 3]
[(#\<) 4]))))
(define autocomplete-scores
(map autocomplete-score (filter-not corrupt? (map parse lines))))
(check-equal? (list-ref (sort autocomplete-scores >) (floor (/ (length autocomplete-scores) 2))) 1118645287)