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Permutations: Difference between revisions
→{{header|Common Lisp}}
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(loop for a = "1234" then (next-perm a #'char<) while a do
(write-line a))</lang>
Recursive implementation of Heap's algorithm:
<lang lisp>(defun heap-permutations (seq)
(let ((permutations nil))
(labels ((permute (seq k)
(if (= k 1)
(push seq permutations)
(progn
(permute seq (1- k))
(loop for i from 0 below (1- k) do
(if (evenp k)
(rotatef (elt seq i) (elt seq (1- k)))
(rotatef (elt seq 0) (elt seq (1- k))))
(permute seq (1- k)))))))
(permute seq (length seq))
permutations)))</lang>
=={{header|Crystal}}==
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