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@@ -0,0 +1,76 @@
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+#lang racket
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+
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+(define line
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+ (call-with-input-file "input"
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+ (λ (fp) (read-line fp))))
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+
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+(define strs (string-split line ","))
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+
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+(define (parse-len str)
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+ (define str-len (string-length str))
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+ (define last-char (string-ref str (- str-len 1)))
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+ (if (char=? #\- last-char)
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+ (list (substring str 0 (- str-len 1)) #\-)
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+ (let ()
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+ (define tp (string-split str "="))
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+ (list (car tp) #\= (string->number (cadr tp))))))
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+
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+(define (calc-hash str)
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+ (define len (string-length str))
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+ (let loop ((i 0) (cur 0))
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+ (if (< i len)
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+ (let ()
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+ (define c (string-ref str i))
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+ (define ascii (char->integer c))
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+ (loop (+ i 1) (modulo (* 17 (+ cur ascii)) 256)))
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+ cur)))
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+
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+(define (remove-len lst lable)
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+ (let loop ((cur lst) (ret '()))
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+ (if (null? cur)
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+ (reverse ret)
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+ (if (equal? (caar cur) lable)
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+ (loop (cdr cur) ret)
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+ (loop (cdr cur) (cons (car cur) ret))))))
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+
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+(define (insert-len lst lable value)
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+ (let loop ((cur lst) (ret '()) (inserted #f))
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+ (if (null? cur)
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+ (if inserted
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+ (reverse ret)
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+ (reverse (cons (cons lable value) ret)))
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+ (if (equal? (caar cur) lable)
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+ (loop (cdr cur) (cons (cons lable value) ret) #t)
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+ (loop (cdr cur) (cons (car cur) ret) inserted)))))
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+
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+(define boxes (make-vector 256 '()))
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+
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+(define lens (map parse-len strs))
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+
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+(define (process-len len box)
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+ (if (char=? #\- (cadr len))
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+ (remove-len box (car len))
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+ (insert-len box (car len) (caddr len))))
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+
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+;; do lens installation
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+(let loop ((cur lens))
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+ (if (null? cur)
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+ (void)
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+ (let ()
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+ (define lable (caar cur))
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+ (define hash-num (calc-hash lable))
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+ (vector-set! boxes hash-num (process-len (car cur) (vector-ref boxes hash-num)))
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+ (loop (cdr cur)))))
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+
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+;; calculate focusing power
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+(let loop ((i 1) (ret 0))
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+ (if (> i 256)
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+ ret
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+ (let ()
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+ (define box (vector-ref boxes (- i 1)))
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+ (define sum
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+ (let loop ((j 1) (cur box) (s 0))
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+ (if (null? cur)
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+ s
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+ (loop (+ j 1) (cdr cur) (+ s (* i j (cdar cur)))))))
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+ (loop (+ i 1) (+ ret sum)))))
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