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Longest common subsequence: Difference between revisions
→{{header|Common Lisp}}
Line 447:
<lang lisp>"123"
3</lang>
===An alternative adopted from Clojure===
Here is another version with its own memoization macro:
<lang lisp>(defmacro mem-defun (name args body)
(let ((hash-name (gensym)))
`(let ((,hash-name (make-hash-table :test 'equal)))
(defun ,name ,args
(or (gethash (list ,@args) ,hash-name)
(setf (gethash (list ,@args) ,hash-name)
,body))))))
(mem-defun lcs (xs ys)
(labels ((longer (a b) (if (> (length a) (length b)) a b)))
(cond ((or (null xs) (null ys)) nil)
((equal (car xs) (car ys)) (cons (car xs) (lcs (cdr xs) (cdr ys))))
(t (longer (lcs (cdr xs) ys)
(lcs xs (cdr ys)))))))</lang>
When we test it, we get:
<lang lisp>(coerce (lcs (coerce "thisisatest" 'list) (coerce "testing123testing" 'list)) 'string))))
"tsitest"</lang>
=={{header|D}}==
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