Your permutations is being called again for similar inputs..
Try using this and see that similar inputs like (2 3) are coming again for
(permutations [1 2 3 4])
(defn permutations [s]
(prn s) ;; This will print input
(lazy-seq
(if (seq (rest s))
(apply concat (for [x s]
(map #(cons x %) (permutations (remove #{x} s)))))
[s])))
Using the following solves that problem : It seems to be also not taking
much memory :
(defn insert-at-every-pos [x v]
(loop [s x
e []
r []]
(if (empty? s)
(conj r (into [v] x))
(recur (pop s) (conj e (peek s)) (conj r (into (conj s v) e))))))
(defn permutations [s]
(prn s)
(lazy-seq
(if (seq (rest s))
(mapcat (fn [p] (insert-at-every-pos p (peek s))) (permutations (pop
s)))
[s])))
(filter nil? (permutations (vec (range 11))))
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