93 lines
2.3 KiB
Racket
93 lines
2.3 KiB
Racket
#lang racket
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(require "../lib.rkt")
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(define test
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'("30373"
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"25512"
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"65332"
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"33549"
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"35390"))
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(define input
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(~>> (problem-input 8) #;test
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(map string->list)
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(mmap char->number)
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(map list->vector)
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list->vector))
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(define (get-tree r c)
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(vector-ref (vector-ref input r) c))
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(define width (vector-length (vector-first input)))
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(define height (vector-length input))
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(define (part1)
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(define talls (mutable-set))
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(for ([r (range height)])
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(set-add! talls (cons r 0))
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(set-add! talls (cons r (sub1 width)))
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(for/fold ([tallest (get-tree r 0)])
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([c (range width)])
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(define t (get-tree r c))
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(if (< tallest t)
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(begin (set-add! talls (cons r c)) t)
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tallest))
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(for/fold ([tallest (get-tree r (sub1 width))])
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([c (reverse (range width))])
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(define t (get-tree r c))
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(if (< tallest t)
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(begin (set-add! talls (cons r c)) t)
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tallest)))
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(for ([c (range width)])
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(set-add! talls (cons 0 c))
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(set-add! talls (cons (sub1 height) c))
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(for/fold ([tallest (get-tree 0 c)])
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([r (range height)])
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(define t (get-tree r c))
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(if (< tallest t)
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(begin (set-add! talls (cons r c)) t)
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tallest))
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(for/fold ([tallest (get-tree (sub1 height) c)])
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([r (reverse (range height))])
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(define t (get-tree r c))
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(if (< tallest t)
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(begin (set-add! talls (cons r c)) t)
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tallest)))
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(set-count talls))
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(define (score r c)
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(define t (get-tree r c))
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(define s1
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(let loop ([c* (add1 c)])
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(if (or (>= c* (sub1 width))
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(>= (get-tree r c*) t))
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(- c* c)
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(loop (add1 c*)))))
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(define s2
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(let loop ([c* (sub1 c)])
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(if (or (<= c* 0)
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(>= (get-tree r c*) t))
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(- c c*)
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(loop (sub1 c*)))))
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(define s3
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(let loop ([r* (add1 r)])
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(if (or (>= r* (sub1 height))
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(>= (get-tree r* c) t))
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(- r* r)
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(loop (add1 r*)))))
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(define s4
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(let loop ([r* (sub1 r)])
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(if (or (<= r* 0)
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(>= (get-tree r* c) t))
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(- r r*)
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(loop (sub1 r*)))))
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(* s1 s2 s3 s4))
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(define part2
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(maximum
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(for*/list ([r (range 1 (sub1 height))]
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[c (range 1 (sub1 width))])
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(score r c))))
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(show-solution (part1) part2) |