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Dimitri Lozeve 2024-11-12 21:43:32 +01:00
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#lang racket
(module+ test
(require rackunit))
(module+ main
(displayln "Day 12"))
(define (parse-instruction str)
(list (string->symbol (substring str 0 1))
(string->number (substring str 1))))
(define (read-input filename)
(map parse-instruction (file->lines filename)))
(struct state
(pos dir)
#:transparent)
(define (step st instr)
(match instr
[`(N ,n) (struct-copy state st [pos (+ (state-pos st) (make-rectangular 0 n))])]
[`(S ,n) (struct-copy state st [pos (- (state-pos st) (make-rectangular 0 n))])]
[`(E ,n) (struct-copy state st [pos (+ (state-pos st) (make-rectangular n 0))])]
[`(W ,n) (struct-copy state st [pos (- (state-pos st) (make-rectangular n 0))])]
[`(F ,n) (struct-copy state st [pos (+ (state-pos st) (* n (state-dir st)))])]
[`(R ,n) (struct-copy state st [dir (* (state-dir st) (make-polar 1 (degrees->radians (- n))))])]
[`(L ,n) (struct-copy state st [dir (* (state-dir st) (make-polar 1 (degrees->radians n)))])]))
(define (part1 filename)
(define input (read-input filename))
(define final
(state-pos (for/fold ([st (state 0 1)])
([instr (in-list input)])
(step st instr))))
(exact-round (+ (abs (real-part final)) (abs (imag-part final)))))
(module+ test
(check-equal? (part1 "test") 25))
(module+ main
(displayln (part1 "input")))
(define (step2 st instr)
(match instr
[`(N ,n) (struct-copy state st [dir (+ (state-dir st) (make-rectangular 0 n))])]
[`(S ,n) (struct-copy state st [dir (- (state-dir st) (make-rectangular 0 n))])]
[`(E ,n) (struct-copy state st [dir (+ (state-dir st) (make-rectangular n 0))])]
[`(W ,n) (struct-copy state st [dir (- (state-dir st) (make-rectangular n 0))])]
[`(F ,n) (struct-copy state st [pos (+ (state-pos st) (* n (state-dir st)))])]
[`(R ,n) (struct-copy state st [dir (* (state-dir st) (make-polar 1 (degrees->radians (- n))))])]
[`(L ,n) (struct-copy state st [dir (* (state-dir st) (make-polar 1 (degrees->radians n)))])]))
(define (part2 filename)
(define input (read-input filename))
(define final
(state-pos (for/fold ([st (state 0 (make-rectangular 10 1))])
([instr (in-list input)])
(step2 st instr))))
(exact-round (+ (abs (real-part final)) (abs (imag-part final)))))
(module+ test
(check-equal? (part2 "test") 286))
(module+ main
(displayln (part2 "input")))