June 2018 Update

Task/Multiplicative-order/Clojure/multiplicative-order.clj

@@ -0,0 +1,26 @@
+(defn gcd [a b]
+   (if (zero? b)
+      a
+      (recur b (mod a b))))
+
+(defn lcm [a b]
+   (/ (* a b) (gcd a b)))
+
+(def NaN  (Math/log -1))
+
+(defn ord' [a [p e]]
+   (let [m   (imath/expt p e)
+         t   (* (quot m p) (dec p))]
+            (loop [dv (factor/divisors t)]
+               (let [d (first dv)]
+                  (if (= (mmath/expm a d m) 1)
+                     d
+                     (recur (next dv)))))))
+
+(defn ord [a n]
+   (if (not= (gcd a n) 1)
+      NaN
+      (->>
+         (factor/factorize n)
+         (map (partial ord' a))
+         (reduce lcm))))