http://adventofcode.com/2017/day/6

day6.el

(defun find-idx-of-max (list)
  (let ((max_i 0) (val) (max))
    (dotimes (i (length list) max_i)
      (setq val (nth i list))
      (setq max (nth max_i list))
      (when (> val max) (setq max_i i))
      )
    )
  )

(defun cycle-list (list start_i v)
  (let ((i start_i) (val v))
    (setf (nth i list) 0)
    (setq i (1+ i))
    (when (>= i (length list)) (setq i 0))
    (while (> val 0)
      (setf (nth i list) (1+ (nth i list)))
      (setq val (1- val))
      (setq i (1+ i))
      (when (>= i (length list)) (setq i 0))
      )
    list
    )
  )

(defun reallocate-step (list)
  (let ((n (length list)) i val rem)
    (setq i (find-idx-of-max list))
    (cycle-list list i (nth i list))
   )
  list
  )

(defun get-pos (element list)
  (let (idxs val)
    (catch 'break
      (dotimes (i (length list))
        (setq val (nth i list))
        (when (equal element val) (throw 'break i))
        )
      )
    )
  )

(get-pos 2 '(1 1 2)) ;; 2

(defun reallocate (list)
  (let ((s 1) (results))
    (reallocate-step list)
    (while (and (not (member list results)) (< s 10000))
      (push (copy-sequence list) results)
      (reallocate-step list)
      (setq s (1+ s))
      )
    (print results)
    (print (format "Part #1: %d" s))
    (print (format "Part #2: %d" (- (length results) (get-pos list (reverse results)))))
    )
  )

(reallocate '(0 2 7 0)) ;; 5
(reallocate-step '(0 2 7 0)) ;; 2 4 1 2
(reallocate-step '(3 1 2 3)) ;; 0 2 3 4
(reallocate-step '(0 2 3 4)) ;; 1 3 1 4
(reallocate-step '(1 3 1 4)) ;; 1 3 1 4
(reallocate-step '(4 1 15	12 0 9 9 5 5 8 7 3 14	5	12 3)) ;; 5 2 0 13 1 10 10 6 6 9 8 4 15	6	13 4
(reallocate '(4 1 15 12 0 9 9 5 5 8 7 3 14 5 12 3))

(find-idx-of-max '(7 3 2 19 20)) ;; 4

(cycle-list '(0 2 7 0) 2 2 1) ;; 2 4 1 2