44 lines
1.4 KiB
Racket
44 lines
1.4 KiB
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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;; helper functions here
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;; linear time sum checker, assuming sorted subrange
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(define (contains-sum? vec start end wanted-sum)
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(define (helper [a start] [b (sub1 end)])
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(define cur-sum (+ (vector-ref vec a) (vector-ref vec b)))
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(cond
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[(>= a b) #f]
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[(= cur-sum wanted-sum) #t]
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[(< cur-sum wanted-sum) (helper (add1 a) b)]
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[(> cur-sum wanted-sum) (helper a (sub1 b))]))
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(vector-sort! vec < start end)
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(helper))
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;; continuously sort the part of the vector below the iterator, and call contains-sum?
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(define (part1 vec)
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(for*/first ([i (in-range 25 (vector-length vec))] [x (in-value (vector-ref vec i))]
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#:unless (contains-sum? (vector-copy vec (- i 25) i) 0 25 x))
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(cons i x)))
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(define (part2 vec pt1-ans)
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(match-define (cons pt1-i pt1-val) pt1-ans)
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(for*/first ([ct (in-range 3 100)] [i (in-range 0 (- pt1-i ct))]
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[sub (in-value (vector-copy vec i (+ i ct)))]
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#:when (= pt1-val (for/fold ([x 0]) ([v (in-vector sub)]) (+ x v))))
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(+ (vector-argmin identity sub) (vector-argmax identity sub))))
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(module+ main
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(define input (list->vector (file->list "inputs/9")))
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;; part 1
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(define pt1 (part1 (vector-copy input)))
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(answer 9 1 (cdr pt1))
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;; part 2
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(answer 9 2 (part2 (vector-copy input) pt1))
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(displayln "meow"))
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