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adventofcode
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Day 20

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Jonathan Chan 2022-12-19 22:57:09 -08:00
parent 657d532177
commit 3e3a03e517
2 changed files with 5063 additions and 0 deletions
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input/20.txt Normal file
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src/20.rkt Normal file
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#lang curly-fn racket
(require "../lib.rkt")
(define input
(map string->number (problem-input 20)))
(struct element (value [prev #:mutable] [next #:mutable]))
(define (parse)
(let ([hd (element (first input) #f #f)])
(for/fold ([curr hd]
[elements `(,hd)]
#:result (values (begin (set-element-next! curr hd)
(set-element-prev! hd curr)
(reverse elements))))
([i (rest input)])
(define next (element i curr #f))
(set-element-next! curr next)
(values next (cons next elements)))))
(define (mix! elements key)
(for ([e elements])
(set-element-next! (element-prev e) (element-next e))
(set-element-prev! (element-next e) (element-prev e))
(let loop ([i (% (* (element-value e) key) (sub1 (length elements)))]
[next (element-next e)])
(cond
[(zero? i)
(set-element-next! (element-prev next) e)
(set-element-prev! e (element-prev next))
(set-element-next! e next)
(set-element-prev! next e)]
[(positive? i) (loop (sub1 i) (element-next next))]
[(negative? i) (loop (add1 i) (element-prev next))]))))
(define (grove elements key)
(define 0th
(let loop ([curr (first elements)])
(if (= (element-value curr) 0)
curr
(loop (element-next curr)))))
(define (get e i)
(for/fold ([curr e])
([_ (in-range i)])
(element-next curr)))
(* (+ (element-value (get 0th (% 1000 (sub1 (length elements)))))
(element-value (get 0th (% 2000 (sub1 (length elements)))))
(element-value (get 0th (% 3000 (sub1 (length elements))))))
key))
(define part1
(let ([elements (parse)])
(mix! elements 1)
(grove elements 1)))
(define part2
(let ([elements (parse)])
(for ([_ (in-range 10)])
(mix! elements 811589153))
(grove elements 811589153)))
(show-solution part1 part2)