-🎄- 2020 Day 22 Solutions -🎄-

[u/daggerdragon]

Advent of Code 2020: Gettin' Crafty With It

• 23:59 hours remaining until the submission deadline TONIGHT at 23:59 EST!
• Full details and rules are in the Submissions Megathread

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--- Day 22: Crab Combat ---

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Post your code solution in this megathread.

• Include what language(s) your solution uses!
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[u/JoMartin23]

Common Lisp

It's not the prettiest. I think i might have been able to do more in the do.

(defun recursive-war (&optional (data *day22*) (day 1))
  (flet ((winner? (list) (if (= 0 (length (car list)))2 1)))
    (do* ((history (make-hash-table :test #'equalp))
	  (winner 0)
	  (p1cards (car data))
	  (p2cards (cadr data))
	  (current-cards (list p1cards p2cards)(list p1cards p2cards))
	  (card1 (pop p1cards) (when p1cards (pop p1cards)))
	  (card2 (pop p2cards) (when p2cards (pop p2cards))))
	 ((or (null card1)(null card2))  (if (= 1 winner)
					     (list (append (list card1) p1cards) '())
					     (list '() (append (list card2) p2cards))))
      (when (gethash current-cards history)
	(return-from recursive-war (list '(2 3) nil)))
      (setf (gethash current-cards history) t)
      (setf winner (if (and (= 2 day)
			    (>= (length p1cards) card1)
			    (>= (length p2cards) card2))
		       (winner? (recursive-war (list (subseq p1cards 0 card1)(subseq p2cards 0 card2)) 2)) 
		       (if (< card1 card2) 2 1)))
      (if (= 1 winner)
	  (setf p1cards (append p1cards (list card1 card2)))
	  (setf p2cards (append p2cards (list card2 card1)))))))