Data commit

Task/Permutations/Clojure/permutations-1.clj

@@ -0,0 +1,4 @@
+user=> (require 'clojure.contrib.combinatorics)
+nil
+user=> (clojure.contrib.combinatorics/permutations [1 2 3])
+((1 2 3) (1 3 2) (2 1 3) (2 3 1) (3 1 2) (3 2 1))

Task/Permutations/Clojure/permutations-2.clj

@@ -0,0 +1,35 @@
+(defn- iter-perm [v]
+  (let [len (count v),
+	j (loop [i (- len 2)]
+	     (cond (= i -1) nil
+		   (< (v i) (v (inc i))) i
+		   :else (recur (dec i))))]
+    (when j
+      (let [vj (v j),
+	    l (loop [i (dec len)]
+		(if (< vj (v i)) i (recur (dec i))))]
+	(loop [v (assoc v j (v l) l vj), k (inc j), l (dec len)]
+	  (if (< k l)
+	    (recur (assoc v k (v l) l (v k)) (inc k) (dec l))
+	    v))))))
+
+
+(defn- vec-lex-permutations [v]
+  (when v (cons v (lazy-seq (vec-lex-permutations (iter-perm v))))))
+
+(defn lex-permutations
+  "Fast lexicographic permutation generator for a sequence of numbers"
+  [c]
+  (lazy-seq
+   (let [vec-sorted (vec (sort c))]
+     (if (zero? (count vec-sorted))
+       (list [])
+       (vec-lex-permutations vec-sorted)))))
+
+(defn permutations
+  "All the permutations of items, lexicographic by index"
+  [items]
+  (let [v (vec items)]
+    (map #(map v %) (lex-permutations (range (count v))))))
+
+(println (permutations [1 2 3]))