52 lines
1.1 KiB
Racket
52 lines
1.1 KiB
Racket
#lang racket
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(module+ test
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(require rackunit))
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(module+ main
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(displayln "Day 3"))
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(define (parse-line str)
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(list->vector
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(map (λ (c) (if (equal? c #\#) 1 0)) (string->list str))))
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(define (read-input filename)
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(with-input-from-file filename
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(lambda ()
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(for/vector ([line (in-lines)])
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(parse-line line)))))
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(define (traj grid down right)
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(define height (vector-length grid))
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(define width (vector-length (vector-ref grid 0)))
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(for/list ([line (in-vector grid 0 #f down)]
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[j (in-range 0 (* width height right) right)])
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(vector-ref line (remainder j width))))
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(define (part1 filename)
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(define grid (read-input filename))
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(apply + (traj grid 1 3)))
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(module+ test
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(check-equal? (part1 "test") 7))
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(module+ main
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(displayln (part1 "input")))
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(define slopes
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'((1 1)
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(1 3)
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(1 5)
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(1 7)
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(2 1)))
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(define (part2 filename)
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(define grid (read-input filename))
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(for/product ([slope slopes])
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(apply + (traj grid (car slope) (cadr slope)))))
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(module+ test
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(check-equal? (part2 "test") 336))
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(module+ main
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(displayln (part2 "input")))
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