diff options
Diffstat (limited to '2021')
| -rw-r--r-- | 2021/day-16/day-16.rkt | 84 |
1 files changed, 64 insertions, 20 deletions
diff --git a/2021/day-16/day-16.rkt b/2021/day-16/day-16.rkt index 80c2a54..c860e27 100644 --- a/2021/day-16/day-16.rkt +++ b/2021/day-16/day-16.rkt @@ -1,30 +1,74 @@ #lang racket (require "../../jj-aoc.rkt" + bitsyntax threading) +(struct packet (version id type value size) + #:transparent) + +(define (BITS->bitstring str) + (integer->bit-string (string->number str 16) + (* 4 (string-length str)) + #true)) + (define data (~> (open-day 16 2021) port->string string-trim - string->list)) + BITS->bitstring)) + +(define (overflow l w) + (define extra (modulo l 4)) + (if (= extra 0) 0 (- w extra))) + +(define (get-literal-contents bitstr) + (for/fold ([assembled (bit-string)] + [remaining bitstr] + [total-length 6] + [complete? #f] + #:result (list (bit-string->integer assembled #t #f) + total-length + remaining)) + ([_ (in-naturals)] + #:break complete?) + (bit-string-case remaining + ([(= 1 :: bits 1) (number :: bits 4) (remaining :: binary)] + (values (bit-string-append assembled (integer->bit-string number 4 #t)) + remaining + (+ total-length 5) + #f)) + ([(= 0 :: bits 1) + (number :: bits 4) + (ignored :: bits (overflow (+ total-length 5) 4)) + (remaining :: binary)] + (values (bit-string-append assembled (integer->bit-string number 4 #t)) + remaining + (+ total-length 5) + #t))))) -(define (hex->bin h) - (match h - [#\0 '(0 0 0 0)] - [#\1 '(0 0 0 1)] - [#\2 '(0 0 1 0)] - [#\3 '(0 0 1 1)] - [#\4 '(0 1 0 0)] - [#\5 '(0 1 0 1)] - [#\6 '(0 1 1 0)] - [#\7 '(0 1 1 1)] - [#\8 '(1 0 0 0)] - [#\9 '(1 0 0 1)] - [#\A '(1 0 1 0)] - [#\B '(1 0 1 1)] - [#\C '(1 1 0 0)] - [#\D '(1 1 0 1)] - [#\E '(1 1 1 0)] - [#\F '(1 1 1 1)])) +(define (identify-next-packet bitstr) + (bit-string-case bitstr + ([(packet-version :: bits 3) + (= 4 :: bits 3) + (remaining :: binary)] + (match-define (list n packet-length next-bitstr) (get-literal-contents remaining)) + (list (packet packet-version + 4 + 'literal + n + packet-length) + next-bitstr)) + ([(packet-version :: bits 3) + (type-id :: bits 3) + (= 0 :: bits 1) + (subpacket-length :: bits 15) + (remaining :: binary)] + (list (packet packet-version type-id 'type-0-operator 0 0) remaining)) + ([(packet-version :: bits 3) + (type-id :: bits 3) + (= 1 :: bits 1) + (subpacket-count :: bits 11) + (remaining :: binary)] + (list (packet packet-version type-id 'type-1-operator 0 0) remaining)))) -(map hex->bin data)
\ No newline at end of file +(identify-next-packet (BITS->bitstring "D2FE28")) |