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Task/Digital-root-Multiplicative-digital-root/Ruby/digital-root-multiplicative-digital-root.rb

@@ -0,0 +1,19 @@
+def mdroot(n)
+  mdr, persist = n, 0
+  until mdr < 10 do
+    mdr = mdr.to_s.each_char.map(&:to_i).inject(:*)
+    persist += 1
+  end
+  [mdr, persist]
+end
+
+puts "Number: MDR  MP", "======  ===  =="
+[123321, 7739, 893, 899998].each{|n| puts "%6d:   %d  %2d" % [n, *mdroot(n)]}
+
+counter = Hash.new{|h,k| h[k]=[]}
+0.step do |i|
+  counter[mdroot(i).first] << i
+  break if counter.values.all?{|v| v.size >= 5 }
+end
+puts "", "MDR: [n0..n4]", "===  ========"
+10.times{|i| puts "%3d: %p" % [i, counter[i].first(5)]}