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49 lines
1.3 KiB
Racket
49 lines
1.3 KiB
Racket
#lang br
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(require racket/file rackunit)
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(match-define (list low high)
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(map string->number (string-split (file->string "04.rktd") "-")))
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(define (double-digit? num)
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(define numstr (number->string num))
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(match (for/list ([c0 (in-string numstr)]
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[c1 (in-string numstr 1)]
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#:when (char=? c0 c1))
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(string->number (string c0)))
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[(? null?) #false]
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[nums nums]))
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(define (num->digits num)
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(for/list ([c (in-string (number->string num))])
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(string->number (string c))))
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(define (monotonic? num)
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(apply <= (num->digits num)))
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;; 1
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(check-eq?
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(for/sum ([num (in-range low (add1 high))]
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#:when (and (double-digit? num) (monotonic? num)))
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1)
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1079)
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(define (triple-digit? num digit)
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(define numstr (number->string num))
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(define digitc (car (string->list (number->string digit))))
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(for/or ([c0 (in-string numstr)]
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[c1 (in-string numstr 1)]
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[c2 (in-string numstr 2)])
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(char=? c0 c1 c2 digitc)))
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;;2
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(check-eq?
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(for/sum ([num (in-range low (add1 high))]
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#:when (and (for/or ([digits (in-value (double-digit? num))]
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#:when digits
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[digit (in-list digits)])
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(not (triple-digit? num digit)))
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(monotonic? num)))
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1)
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699)
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