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#lang racket
(require "../lib/utils.rkt")
(define lines
(call-with-input-file "input"
(λ (fp)
(get-lines fp))))
(define (parse-data line)
(map string->number (string-split line)))
(define data (map parse-data lines))
(define (diff lst)
(let loop ((cur lst) (ret '()))
(if (or (null? cur) (null? (cdr cur)))
(reverse ret)
(loop (cdr cur) (cons (- (cadr cur) (car cur)) ret)))))
(define (predict lst)
(if (andmap (λ (x) (= x (car lst))) lst)
(car lst)
(- (car lst) (predict (diff lst)))))
(apply + (map predict data))
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