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Refactored Day 9.

This commit is contained in:
Jonathan Chan 2020-12-10 00:42:27 -08:00 committed by Jonathan Chan
parent 38209a6ce6
commit 5706b2c671
1 changed files with 16 additions and 12 deletions
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28
src/09.rkt
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@ -3,25 +3,29 @@
(require "../lib.rkt")
(define input (map string->number (problem-input 9)))
(define input* (list->vector input))
(define (pair-sum lst target)
(for*/or ([i lst]
[j lst])
(= (+ i j) target)))
(define (pair-sum start end)
(for*/or ([i (range start end)]
[j (range start end)])
(= (vector-ref input* end)
(+ (vector-ref input* i)
(vector-ref input* j)))))
(define part1
(let loop ([current (take input 25)] [next (list-ref input 25)] [remain (drop input 26)])
(if (pair-sum current next)
(loop (snoc (rest current) next) (first remain) (rest remain))
next)))
(let loop ([start 0] [end 25])
(if (pair-sum start end)
(loop (add1 start) (add1 end))
(vector-ref input* end))))
(define part2
(let loop ([current '()] [remain input] [sum 0])
(let loop ([start 0] [end 0] [sum 0])
(cond
[(< sum part1)
(loop (snoc current (first remain)) (rest remain) (+ sum (first remain)))]
(loop start (add1 end) (+ sum (vector-ref input* end)))]
[(> sum part1)
(loop (rest current) remain (- sum (first current)))]
[else (+ (apply min current) (apply max current))])))
(loop (add1 start) end (- sum (vector-ref input* start)))]
[else (let ([contig (drop (take input end) start)])
(+ (apply min contig) (apply max contig)))])))
(show-solution part1 part2)