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(import (chicken io))
(import (chicken string))
(import srfi-69)
(import srfi-1)
(define (read-input)
(with-input-from-file "input"
(lambda ()
(define part1
(let loop ((ret '()))
(let ((line (read-line)))
(if (= 0 (string-length line))
(reverse ret)
(loop (cons line ret))))))
(define part2
(let loop ((ret '()))
(let ((line (read-line)))
(if (eof-object? line)
(reverse ret)
(loop (cons line ret))))))
(values part1 part2))))
(define-values (part1 part2) (read-input))
(set! part1 (map (lambda (x) (string-split x "|")) part1))
(set! part1 (map (lambda (x) (map string->number x)) part1))
(define rules (make-hash-table))
(map (lambda (x)
(hash-table-set! rules x #t) '())
part1)
(define updates (map (lambda (x) (string-split x ",")) part2))
(set! updates (map (lambda (x) (map string->number x)) updates))
(define (check-rules x lst)
(if (null? lst)
#t
(and (not (hash-table-ref/default rules (list (car lst) x) #f))
(check-rules x (cdr lst)))))
(define (find-failed x lst)
(if (null? lst)
#f
(if (hash-table-ref/default rules (list (car lst) x) #f)
lst
(find-failed x (cdr lst)))))
(define (check-update update)
(if (null? update)
#t
(and (check-rules (car update) (cdr update))
(check-update (cdr update)))))
(define (correct-update! update)
(if (null? update)
'()
(let ()
(define failed (find-failed (car update) (cdr update)))
(if failed
(let ()
(define tmp (car failed))
(set-car! failed (car update))
(set-car! update tmp))
(correct-update! (cdr update))))))
(define (median lst)
(list-ref lst (quotient (length lst) 2)))
(define incorrect (filter (lambda (x) (not (check-update x))) updates))
(define (do-correction! lst)
(if (check-update lst)
'()
(let ()
(correct-update! lst)
(do-correction! lst))))
(map do-correction! incorrect)
(display (apply + (map median incorrect)))
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