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59 lines
2.1 KiB
Racket
59 lines
2.1 KiB
Racket
3 years ago
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#lang racket
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(define (map-map f lst) ; map . map
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(map (λ (x) (map (λ (y) (f y)) x)) lst))
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(define/match (add-dx-dy points)
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[((list (list x1 y1) (list x2 y2)))
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(let* ([dx (- x2 x1)]
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[dy (- y2 y1)]
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[len (max (abs dx) (abs dy))])
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(list (list x1 y1) (list x2 y2) dx dy len))])
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(define (vectorize line)
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(let* ([parts (string-split line " -> ")] ; '("0,9 -> 5,9") -> '("0,9" "5,9")
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[strings (map (λ (part) (string-split part ",")) parts)] ; '("0,9" "5,9") -> '(("0" "9") ("5" "9"))
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[nums (map-map string->number strings)] ; '(("0" "9") ("5" "9")) -> '((0 9) (5 9))
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[vectors (add-dx-dy nums)]) ; '((x1 y2) (x2 y2) dx dy length)
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vectors))
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(define/match (non-diagonal? vect)
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[((list _ _ dx dy _)) (or (= dx 0) (= dy 0))])
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(define/match (get-points-from-vect vect) ; takes vect '((x1 y1) (x2 y2) dx dy len) and returns a list of points it hits '((x1 y1) (x2 y2) ..)
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[((list (list x1 y1) (list x2 y2) dx dy len))
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(let loop ([i len])
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(if (= i 0) ; at the end
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(list (list x1 y1)) ; return this point
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(append (list (list (+ x1 (/ (* dx i) len)) (+ y1 (/ (* dy i) len)))) ; return the next point..
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(loop (sub1 i)))))]) ; appended to the result of recursing with i - 1
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(define (add-point ht point)
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(let ([dups (hash-ref ht point 0)])
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(hash-set! ht point (+ 1 dups))))
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(define (travel-and-add ht vects)
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(for ([i (in-list vects)])
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(let ([points (get-points-from-vect i)])
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(map (λ (p) (add-point ht p)) points))))
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(define part1
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(let* ([lines (file->lines "day5.txt")]
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[vectors (map vectorize lines)]
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[non-diagonals (filter non-diagonal? vectors)]
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[ht (make-hash)]
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[points-hit (travel-and-add ht non-diagonals)]
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[counts (hash-values ht)])
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(length (filter (λ (x) (> x 1)) counts))))
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part1
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(define part2
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(let* ([lines (file->lines "day5.txt")]
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[vectors (map vectorize lines)]
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[ht (make-hash)]
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[points-hit (travel-and-add ht vectors)]
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[counts (hash-values ht)])
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(length (filter (λ (x) (> x 1)) counts))))
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part2
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