36 lines
1007 B
Racket
36 lines
1007 B
Racket
#lang curly-fn racket
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(require "scripts/aoc.rkt")
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;; solution for day 9
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(define (list-differences lst)
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(for/list ([a (in-list lst)] [b (in-list (rest lst))])
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(- b a)))
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(define (extrapolate lst [arith-func +] [list-func last] [combine-func append])
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(cond
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[(for/and ([x (in-list lst)]) (zero? x)) lst]
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[else
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(define diffs (list-differences lst))
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(define next-layer (extrapolate diffs arith-func list-func combine-func))
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(combine-func lst (list (arith-func (list-func lst) (list-func next-layer))))]))
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(define (part1 input)
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(for/sum ([line (in-list input)])
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(last (extrapolate line))))
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(define (part2 input)
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(for/sum ([line (in-list input)])
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(first (extrapolate line - first #{append %2 %1}))))
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(define (parse fname)
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(for/list ([line (in-list (file->lines fname))])
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(map string->number (string-split line))))
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(module+ main
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(define input (parse "inputs/9"))
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(answer 9 1 (time (part1 input)))
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(answer 9 2 (time (part2 input)))
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(displayln "meow"))
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