24 lines
892 B
Common Lisp
24 lines
892 B
Common Lisp
(defun group-similar (sequence &key (test 'eql))
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(loop for x in (rest sequence)
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with temp = (subseq sequence 0 1)
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if (funcall test (first temp) x)
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do (push x temp)
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else
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collect temp
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and do (setf temp (list x))))
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(defun run-length-encode (sequence)
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(mapcar (lambda (group) (list (first group) (length group)))
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(group-similar (coerce sequence 'list))))
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(defun run-length-decode (sequence)
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(reduce (lambda (s1 s2) (concatenate 'simple-string s1 s2))
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(mapcar (lambda (elem)
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(make-string (second elem)
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:initial-element
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(first elem)))
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sequence)))
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(run-length-encode "WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW")
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(run-length-decode '((#\W 12) (#\B 1) (#\W 12) (#\B 3) (#\W 24) (#\B 1)))
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