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#lang racket
(define/contract (count-students students sandwiches)
(-> (listof exact-integer?) (listof exact-integer?) exact-integer?)
(for/fold ([sandwich-pile sandwiches]
[student-line students]
[remaining-students (length students)]
[break? #false]
#:result remaining-students)
([i (in-naturals)]
#:break break?)
(cond [(and (empty? sandwich-pile)
(empty? student-line))
(values void
void
remaining-students
#true)]
[(equal? (car sandwich-pile)
(car student-line))
(values (cdr sandwich-pile)
(cdr student-line)
(sub1 remaining-students)
#false)]
[(and (not (equal? (list (car sandwich-pile))
(remove-duplicates student-line)))
(= 1 (length (remove-duplicates student-line))))
(values void
void
remaining-students
#true)]
[else
(values sandwich-pile
(append (cdr student-line) (list (car student-line)))
remaining-students
#false)])))
(count-students '(1 1 0 0) '(0 1 0 1))
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