68 lines
2.0 KiB
Racket
68 lines
2.0 KiB
Racket
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#lang curly-fn racket
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(require threading
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"../lib.rkt")
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(define (parse line)
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(match line
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[(regexp #px"([NESWLRF])(\\d+)" (list _ dir amt))
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(list (string->symbol dir) (string->number amt))]))
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(define input (map parse (problem-input 12)))
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(define (turn curr-dir dir angle)
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(define dirs
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(if (symbol=? dir 'R)
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'(N E S W)
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'(N W S E)))
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(define index (index-of dirs curr-dir))
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(list-ref dirs (modulo (+ index (/ angle 90)) 4)))
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(define (rotate x y dir amt)
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(cond
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[(= amt 180) (list (- x) (- y))]
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[(= amt 270) (rotate x y (if (symbol=? dir 'R) 'L 'R) 90)]
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[(symbol=? dir 'R) (list (- y) x)]
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[(symbol=? dir 'L) (list y (- x))]))
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(define (move instr x y dir)
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(match instr
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[`(N ,amt) (values x (- y amt) dir)]
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[`(E ,amt) (values (+ x amt) y dir)]
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[`(S ,amt) (values x (+ y amt) dir)]
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[`(W ,amt) (values (- x amt) y dir)]
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[`(F ,amt) (move `(,dir ,amt) x y dir)]
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[`(,lr ,amt) (values x y (turn dir lr amt))]))
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(define (move* instr x-ship y-ship x-wpt y-wpt)
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(match instr
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[`(N ,amt) (values x-ship y-ship x-wpt (- y-wpt amt))]
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[`(E ,amt) (values x-ship y-ship (+ x-wpt amt) y-wpt)]
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[`(S ,amt) (values x-ship y-ship x-wpt (+ y-wpt amt))]
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[`(W ,amt) (values x-ship y-ship (- x-wpt amt) y-wpt)]
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[`(F ,amt) (values (+ x-ship (* x-wpt amt)) (+ y-ship (* y-wpt amt)) x-wpt y-wpt)]
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[`(,lr ,amt)
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(match-let ([(list x-wpt y-wpt) (rotate x-wpt y-wpt lr amt)])
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(values x-ship y-ship x-wpt y-wpt))]))
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(define (part1)
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(define-values (x y dir)
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(for/fold ([x 0]
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[y 0]
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[dir 'E])
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([instr input])
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(move instr x y dir)))
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(+ (abs x) (abs y)))
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(define (part2)
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(define-values (x-ship y-ship x-wpt y-wpt)
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(for/fold ([x-ship 0]
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[y-ship 0]
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[x-wpt 10]
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[y-wpt -1])
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([instr input])
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(move* instr x-ship y-ship x-wpt y-wpt)))
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(+ (abs x-ship) (abs y-ship)))
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(show-solution (part1) (part2))
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