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42 lines
1.4 KiB
Racket
42 lines
1.4 KiB
Racket
4 years ago
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#lang br
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(require racket/file rackunit racket/dict)
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(define insts
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(for/list ([ln (file->lines "12.rktd")])
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(match-define (list _ name dist) (regexp-match #px"(\\D+)(\\d+)" ln))
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(cons (string->symbol name) (string->number dist))))
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(define left-turn +i)
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(define right-turn -i)
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(define north +i)
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(define east (* north right-turn))
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(define south (* east right-turn))
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(define west (* south right-turn))
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(define (manhattan-dist pos) (+ (abs (real-part pos)) (abs (imag-part pos))))
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(define (solve insts [use-waypoint? #false])
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(for/fold ([pos 0]
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[facing 1]
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[waypoint 10+i]
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#:result (manhattan-dist pos))
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([(name dist) (in-dict insts)])
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(case name
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[(F)
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(define ref-point (if use-waypoint? waypoint facing))
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(values (+ pos (* ref-point dist)) facing waypoint)]
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[(N E S W)
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(define direction (match name
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['S south]
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['N north]
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['E east]
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['W west]))
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(define next-pos (if use-waypoint? pos (+ pos (* direction dist))))
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(values next-pos facing (+ waypoint (* direction dist)))]
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[(L R)
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(define rotation
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(expt (if (eq? name 'L) left-turn right-turn) (/ dist 90)))
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(values pos (* facing rotation) (* waypoint rotation))])))
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(check-equal? (solve insts) 1496)
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(check-equal? (solve insts #t) 63843)
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