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ordnungswidrig/perm.clj

Created December 14, 2010 22:14
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Permutations filtered by predicat
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perm.clj
;;; eager permutations
(defn pop-nth [coll i]
[(nth coll i) (concat (take i coll) (drop (inc i) coll))])
(defn perms [items]
(letfn [(p [previous rest]
(if (empty? rest)
[previous]
(mapcat (fn [i]
(let [[n r] (pop-nth rest i)]
(p (concat previous [n]) r)))
(range (count rest)))))]
(p [] items)))
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