66 lines
2.4 KiB
Racket
66 lines
2.4 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 12"))
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(define (parse-instruction str)
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(list (string->symbol (substring str 0 1))
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(string->number (substring str 1))))
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(define (read-input filename)
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(map parse-instruction (file->lines filename)))
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(struct state
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(pos dir)
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#:transparent)
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(define (step st instr)
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(match instr
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[`(N ,n) (struct-copy state st [pos (+ (state-pos st) (make-rectangular 0 n))])]
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[`(S ,n) (struct-copy state st [pos (- (state-pos st) (make-rectangular 0 n))])]
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[`(E ,n) (struct-copy state st [pos (+ (state-pos st) (make-rectangular n 0))])]
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[`(W ,n) (struct-copy state st [pos (- (state-pos st) (make-rectangular n 0))])]
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[`(F ,n) (struct-copy state st [pos (+ (state-pos st) (* n (state-dir st)))])]
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[`(R ,n) (struct-copy state st [dir (* (state-dir st) (make-polar 1 (degrees->radians (- n))))])]
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[`(L ,n) (struct-copy state st [dir (* (state-dir st) (make-polar 1 (degrees->radians n)))])]))
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(define (part1 filename)
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(define input (read-input filename))
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(define final
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(state-pos (for/fold ([st (state 0 1)])
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([instr (in-list input)])
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(step st instr))))
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(exact-round (+ (abs (real-part final)) (abs (imag-part final)))))
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(module+ test
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(check-equal? (part1 "test") 25))
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(module+ main
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(displayln (part1 "input")))
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(define (step2 st instr)
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(match instr
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[`(N ,n) (struct-copy state st [dir (+ (state-dir st) (make-rectangular 0 n))])]
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[`(S ,n) (struct-copy state st [dir (- (state-dir st) (make-rectangular 0 n))])]
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[`(E ,n) (struct-copy state st [dir (+ (state-dir st) (make-rectangular n 0))])]
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[`(W ,n) (struct-copy state st [dir (- (state-dir st) (make-rectangular n 0))])]
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[`(F ,n) (struct-copy state st [pos (+ (state-pos st) (* n (state-dir st)))])]
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[`(R ,n) (struct-copy state st [dir (* (state-dir st) (make-polar 1 (degrees->radians (- n))))])]
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[`(L ,n) (struct-copy state st [dir (* (state-dir st) (make-polar 1 (degrees->radians n)))])]))
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(define (part2 filename)
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(define input (read-input filename))
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(define final
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(state-pos (for/fold ([st (state 0 (make-rectangular 10 1))])
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([instr (in-list input)])
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(step2 st instr))))
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(exact-round (+ (abs (real-part final)) (abs (imag-part final)))))
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(module+ test
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(check-equal? (part2 "test") 286))
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(module+ main
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(displayln (part2 "input")))
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