You cannot select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
34 lines
1.1 KiB
Racket
34 lines
1.1 KiB
Racket
4 years ago
|
#lang br
|
||
|
|
(require racket/file rackunit)
|
||
|
|
|
||
|
|
(define vec (list->vector (map string->number (file->lines "09.rktd"))))
|
||
|
|
|
||
|
|
(define preamble-length 25)
|
||
|
|
|
||
|
|
(define (idx-valid? idx)
|
||
|
|
(define predecessors (for/list ([val (in-vector vec (- idx preamble-length) idx)])
|
||
|
|
val))
|
||
|
|
(define target (vector-ref vec idx))
|
||
|
|
(for/or ([ints (in-combinations predecessors 2)])
|
||
|
|
(eq? (apply + ints) target)))
|
||
|
|
|
||
|
|
(define invalid-number
|
||
|
|
(for/first ([idx (in-range (add1 preamble-length) (vector-length vec))]
|
||
|
|
#:unless (idx-valid? idx))
|
||
|
|
(vector-ref vec idx)))
|
||
|
|
|
||
|
|
(check-equal? invalid-number 14144619)
|
||
|
|
|
||
|
|
(check-equal?
|
||
|
|
(for/or ([lidx (in-range 0 (vector-length vec))])
|
||
|
|
(let/ec skip-to-next-lidx
|
||
|
|
(for/or ([ridx (in-range (add1 lidx) (vector-length vec))])
|
||
|
|
(define ints (for/list ([val (in-vector vec lidx (add1 ridx))])
|
||
|
|
val))
|
||
|
|
(define sum (apply + ints))
|
||
|
|
(cond
|
||
|
|
[(> sum invalid-number) (skip-to-next-lidx #false)]
|
||
|
|
[(eq? sum invalid-number) (+ (apply min ints) (apply max ints))]
|
||
|
|
[else #false]))))
|
||
|
|
1766397)
|