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;;; https://gitlab.com/Syndamia/senzill
(require :senzill)
(use-package :senzill.math)
(use-package :senzill.collections)
(use-package :senzill.pair)
(use-package :senzill.io)
(ask-for-stream (prog-input)
(let ((rhead '(0 . 0)) (rtail '(0 . 0)) (visited '((0 . 0))) (movec '()))
(flet ((norm>sqrt2p (c) ; If c's eucledian length is less than sqrt(2). In other words, if c is outside the 3x3 square.
"Optimized version of (> (norm p) (sqrt 2))"
(or (> (abs (car c)) 1) (> (abs (cdr c)) 1)))
(dir-to-pair (direction)
(cond ((char= direction #\R) '( 1 . 0))
((char= direction #\L) '(-1 . 0))
((char= direction #\U) '( 0 . 1))
((char= direction #\D) '( 0 . -1)))))
(doread-lines (inpt :read-line-options (prog-input NIL))
(loop for i from 1 to (parse-integer inpt :start 2)
do
(pair+= rhead (dir-to-pair (char inpt 0)))
(setf movec (pair- rhead rtail))
if (norm>sqrt2p movec)
do
;; dist-resize so we don't put the knot on top of the head, but behind it
(pair+= rtail (pair-round (dist-resize-by movec -1)))
(if (not (member-if (lambda (x) (pair= x rtail)) visited))
(push rtail visited))))
(print (length visited)))))
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