use integers

master
Matthew Butterick 5 years ago
parent 6d15732673
commit 43bd2577f8

@ -4,45 +4,40 @@
(match-define (list low high)
(map string->number (string-split (file->string "04.rktd") "-")))
(define (double-digit? num)
(define numstr (number->string num))
(match (for/list ([c0 (in-string numstr)]
[c1 (in-string numstr 1)]
#:when (char=? c0 c1))
(string->number (string c0)))
(define (find-doubles digits)
(match (for/list ([d0 (in-list digits)]
[d1 (in-list (cdr digits))]
#:when (= d0 d1))
d0)
[(? null?) #false]
[nums nums]))
[dds (remove-duplicates dds)]))
(define (num->digits num)
(for/list ([c (in-string (number->string num))])
(string->number (string c))))
(string->number (string c))))
(define (monotonic? num)
(apply <= (num->digits num)))
(define (increasing? digits) (apply <= digits))
;; 1
(check-eq?
(for/sum ([num (in-range low (add1 high))]
#:when (and (double-digit? num) (monotonic? num)))
1)
(for/sum ([digits (in-list (map num->digits (range low (add1 high))))])
(match digits
[(and (? find-doubles) (? increasing?)) 1]
[_ 0]))
1079)
(define (triple-digit? num digit)
(define numstr (number->string num))
(define digitc (car (string->list (number->string digit))))
(for/or ([c0 (in-string numstr)]
[c1 (in-string numstr 1)]
[c2 (in-string numstr 2)])
(char=? c0 c1 c2 digitc)))
(define (triple-digit? ds d)
(and (pair? ds)
(or (list-prefix? (list d d d) ds)
(triple-digit? (cdr ds) d))))
;;2
;; 2
(check-eq?
(for/sum ([num (in-range low (add1 high))]
#:when (and (for/or ([digits (in-value (double-digit? num))]
#:when digits
[digit (in-list digits)])
(not (triple-digit? num digit)))
(monotonic? num)))
1)
(for/sum ([digits (in-list (map num->digits (range low (add1 high))))])
(match digits
[(and (app find-doubles (? list? doubled-digits)) (? increasing?))
#:when (for/or ([dd (in-list doubled-digits)])
(not (triple-digit? digits dd))) 1]
[_ 0]))
699)