47 lines
1.3 KiB
Racket
47 lines
1.3 KiB
Racket
#lang curly-fn racket
|
|
|
|
(require "../lib.rkt")
|
|
|
|
(define input
|
|
(map (match-lambda [(pregexp "(\\w) (\\d+)" `(,_ ,d ,n))
|
|
(list (string->symbol d) (string->number n))])
|
|
(problem-input 9)))
|
|
|
|
(define (sign H T)
|
|
(cond
|
|
[(> H T) 1]
|
|
[(= H T) 0]
|
|
[(< H T) -1]))
|
|
|
|
(define (lead d x y)
|
|
(match d
|
|
['U (values x (add1 y))]
|
|
['D (values x (sub1 y))]
|
|
['R (values (add1 x) y)]
|
|
['L (values (sub1 x) y)]))
|
|
|
|
(define (follow xH yH xT yT)
|
|
(if (or (and (= xH xT) (= (abs (- yH yT)) 2))
|
|
(and (= yH yT) (= (abs (- xH xT)) 2))
|
|
(> (+ (abs (- xH xT)) (abs (- yH yT))) 2))
|
|
(values (+ xT (sign xH xT)) (+ yT (sign yH yT)))
|
|
(values xT yT)))
|
|
|
|
(define (model knots)
|
|
(define visited (mutable-set))
|
|
(for*/fold ([xs (repeat (add1 knots) '(0))]
|
|
[ys (repeat (add1 knots) '(0))])
|
|
([motion input]
|
|
[_ (in-range (second motion))])
|
|
(for/fold ([xs '()] [ys '()]
|
|
#:result (begin (set-add! visited (cons (first xs) (first ys)))
|
|
(values (reverse xs) (reverse ys))))
|
|
([x xs] [y ys])
|
|
(define-values (x* y*)
|
|
(if (empty? xs)
|
|
(lead (first motion) x y)
|
|
(follow (first xs) (first ys) x y)))
|
|
(values (cons x* xs) (cons y* ys))))
|
|
(set-count visited))
|
|
|
|
(show-solution (model 1) (model 9)) |