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52 lines
2.0 KiB
Racket
52 lines
2.0 KiB
Racket
#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 data
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(let* ([input (file->lines "day13.txt")]
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[point-lines (filter (λ (l) (string-contains? l ",")) input)]
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[points (map-map string->number (map (λ (p) (string-split p ",")) point-lines))] ; e.g. '(6 10)
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[fold-lines (filter (λ (l) (string-contains? l "fold")) input)]
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[folds (map (λ (l) (let* ([matches (regexp-match #rx"(.)=(.+)" l)]) ; e.g. '("y" 7)
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(list (second matches) (string->number (third matches))))) fold-lines)])
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(list points folds)))
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(define points (first data))
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(define folds (second data))
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(define (draw points)
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(let* ([width (apply max (map first points))] [height (apply max (map second points))])
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(for-each (λ (row) (begin
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(for-each (λ (col) (printf "~a" (if (member (list col row) points) "#" "."))) (range 0 (+ 1 width)))
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(printf "~n"))) (range 0 (+ 1 height)))))
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(define (move-point point dir loc)
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(let* ([which (if (equal? "x" dir) first second)] ; which coordinate to change. x -> fold left -> change the first digit, etc.
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[diff (* 2 (- (which point) loc))] ; calculate the amount the point should move left/up
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[diffX (if (equal? "x" dir) (λ (x) (- x diff)) identity)]
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[diffY (if (equal? "y" dir) (λ (x) (- x diff)) identity)])
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(if (< (which point) loc) ; if it is below the fold
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point ; just return it
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(list (diffX (first point)) (diffY (second point)))))) ; otherwise, move the point
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(define (fold points f) ; should have picked a different name..
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(let* ([direction (first f)]
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[location (second f)]
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[new-points (map (λ (point) (move-point point direction location)) points)])
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(remove-duplicates new-points)))
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(define part1
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(let* ([first-fold (first folds)]
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[next (fold points first-fold)])
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(length next)))
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part1
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; PART 2
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(define part2
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(draw
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(foldl (λ (f sheet) (fold sheet f)) points folds)))
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part2 |