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;; this one abuses the file format and white space
(ql:quickload :fiveam)
(defun build-stacks (in)
(let* ((input (read-line in))
(stack-amount (ceiling (/ (length input) 4)))
(stacks (make-array stack-amount :initial-element nil)))
(loop for dock = input then (read-line in)
while (not (eq (aref dock 1) #\1))
do (loop
for idx from 0 below stack-amount
for entry = (aref dock (+ 1 (* 4 idx)))
unless (eq entry #\ ) do (push entry (aref stacks idx))))
(map 'vector #'nreverse stacks)))
(defun single-move! (stacks amount from to)
(dotimes (_ amount)
(push (pop (aref stacks from)) (aref stacks to))))
(defun bulk-move! (stacks amount from to)
(setf (aref stacks to)
(append (subseq (aref stacks from) 0 amount)
(aref stacks to)))
(setf (aref stacks from) (subseq (aref stacks from) amount)))
(defun apply-moves (execution in stacks)
(loop for action = (read in nil nil)
while action
do (let ((amount (read in nil nil))
(from (progn (read in nil nil) (1- (read in nil nil))))
(to (progn (read in nil nil) (1- (read in nil nil)))))
(funcall execution stacks amount from to)))
stacks)
(defun solver (execution)
(with-open-file (in "input")
(map 'string #'car
(apply-moves execution in
(build-stacks in)))))
(fiveam:test results
(fiveam:is (equal "TPGVQPFDH" (solver #'single-move!)))
(fiveam:is (equal "DMRDFRHHH" (solver #'bulk-move!))))
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