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#lang racket
(require advent-of-code
threading)
(define data (port->list read (open-aoc-input (find-session) 2022 20 #:cache #true)))
(define gps-lst data)
(define gps-len (length gps-lst))
(define gps-indexed (map cons (inclusive-range 1 gps-len) gps-lst))
(define (mix pt data)
(match-define (list left ... (== pt) right ...) data)
(define start (index-of data pt))
(define move-by (modulo (cdr pt) (sub1 gps-len)))
(cond
[(= 0 move-by) data]
[(<= move-by (length right))
(match-define-values (new-left new-right)
(split-at (append left right) (modulo (+ move-by start) (sub1 gps-len))))
(append new-left (list pt) new-right)]
[else
(match-define-values (new-left new-right)
(split-at (append left right) (modulo (+ move-by start) (sub1 gps-len))))
(append new-left (list pt) new-right)]))
(define (mix-gps data original)
(for/fold ([pts data]) ([pt original])
(mix pt pts)))
(define (cycle-mixed-gps mixed)
(define lst (map cdr mixed))
(in-sequences (drop lst (index-of lst 0)) (in-cycle lst)))
(define (calculate-answer seq)
(for/sum ([id '(1000 2000 3000)]) (sequence-ref seq id)))
;; part 1
(~> gps-indexed (mix-gps _ gps-indexed) cycle-mixed-gps calculate-answer)
;; part 2
(define encrypted-gps-indexed
(for/list ([pt (in-list gps-indexed)] #:do [(match-define (cons i v) pt)])
(cons i (* 811589153 v))))
(~>> encrypted-gps-indexed
((λ (data) (foldr (λ (_ pts) (mix-gps pts data)) data (range 10))))
cycle-mixed-gps
calculate-answer)
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