2016 Update

Task/Multiplicative-order/Ruby/multiplicative-order.rb

@@ -1,16 +1,10 @@
-require 'rational' # for lcm
-require 'mathn'    # for prime_division
+require 'prime'
 
 def powerMod(b, p, m)
-  result = 1
-  bits = p.to_s(2)
-  for bit in bits.split('')
+  p.to_s(2).each_char.inject(1) do |result, bit|
     result = (result * result) % m
-    if bit == '1'
-      result = (result * b) % m
-    end
+    bit=='1' ? (result * b) % m : result
   end
-  result
 end
 
 def multOrder_(a, p, k)
@@ -18,7 +12,7 @@ def multOrder_(a, p, k)
   t = (p - 1) * p ** (k - 1)
   r = 1
   for q, e in t.prime_division
-    x = powerMod(a, t / q ** e, pk)
+    x = powerMod(a, t / q**e, pk)
     while x != 1
       r *= q
       x = powerMod(x, q, pk)
@@ -28,15 +22,15 @@ def multOrder_(a, p, k)
 end
 
 def multOrder(a, m)
-  m.prime_division.inject(1) {|result, f|
+  m.prime_division.inject(1) do |result, f|
     result.lcm(multOrder_(a, *f))
-  }
+  end
 end
 
-puts multOrder(37, 1000)        # 100
+puts multOrder(37, 1000)
 b = 10**20-1
-puts multOrder(2, b) # 3748806900
-puts multOrder(17,b) # 1499522760
+puts multOrder(2, b)
+puts multOrder(17,b)
 b = 100001
 puts multOrder(54,b)
 puts powerMod(54, multOrder(54,b), b)