Initial data commit

Task/Digital-root-Multiplicative-digital-root/Java/digital-root-multiplicative-digital-root.java

@@ -0,0 +1,51 @@
+import java.util.*;
+
+public class MultiplicativeDigitalRoot {
+
+    public static void main(String[] args) {
+
+        System.out.println("NUMBER  MDR   MP");
+        for (long n : new long[]{123321, 7739, 893, 899998}) {
+            long[] a = multiplicativeDigitalRoot(n);
+            System.out.printf("%6d %4d %4d%n", a[0], a[1], a[2]);
+        }
+
+        System.out.println();
+
+        Map<Long, List<Long>> table = new HashMap<>();
+        for (long i = 0; i < 10; i++)
+            table.put(i, new ArrayList<>());
+
+        for (long cnt = 0, n = 0; cnt < 10;) {
+            long[] res = multiplicativeDigitalRoot(n++);
+            List<Long> list = table.get(res[1]);
+            if (list.size() < 5) {
+                list.add(res[0]);
+                cnt = list.size() == 5 ? cnt + 1 : cnt;
+            }
+        }
+
+        System.out.println("MDR: first five numbers with same MDR");
+        table.forEach((key, lst) -> {
+            System.out.printf("%3d: ", key);
+            lst.forEach(e -> System.out.printf("%6s ", e));
+            System.out.println();
+        });
+    }
+
+    public static long[] multiplicativeDigitalRoot(long n) {
+        int mp = 0;
+        long mdr = n;
+        while (mdr > 9) {
+            long m = mdr;
+            long total = 1;
+            while (m > 0) {
+                total *= m % 10;
+                m /= 10;
+            }
+            mdr = total;
+            mp++;
+        }
+        return new long[]{n, mdr, mp};
+    }
+}