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Task/Digital-root-Multiplicative-digital-root/Go/digital-root-multiplicative-digital-root.go

@@ -0,0 +1,55 @@
+package main
+
+import "fmt"
+
+// Only valid for n > 0 && base >= 2
+func mult(n uint64, base int) (mult uint64) {
+	for mult = 1; mult > 0 && n > 0; n /= uint64(base) {
+		mult *= n % uint64(base)
+	}
+	return
+}
+
+// Only valid for n >= 0 && base >= 2
+func MultDigitalRoot(n uint64, base int) (mp, mdr int) {
+	var m uint64
+	for m = n; m >= uint64(base); mp++ {
+		m = mult(m, base)
+	}
+	return mp, int(m)
+}
+
+func main() {
+	const base = 10
+	const size = 5
+
+	const testFmt = "%20v %3v %3v\n"
+	fmt.Printf(testFmt, "Number", "MDR", "MP")
+	for _, n := range [...]uint64{
+		123321, 7739, 893, 899998,
+		18446743999999999999,
+		// From http://mathworld.wolfram.com/MultiplicativePersistence.html
+		3778888999, 277777788888899,
+	} {
+		mp, mdr := MultDigitalRoot(n, base)
+		fmt.Printf(testFmt, n, mdr, mp)
+	}
+	fmt.Println()
+
+	var list [base][]uint64
+	for i := range list {
+		list[i] = make([]uint64, 0, size)
+	}
+	for cnt, n := size*base, uint64(0); cnt > 0; n++ {
+		_, mdr := MultDigitalRoot(n, base)
+		if len(list[mdr]) < size {
+			list[mdr] = append(list[mdr], n)
+			cnt--
+		}
+	}
+	const tableFmt = "%3v: %v\n"
+	fmt.Printf(tableFmt, "MDR", "First")
+	for i, l := range list {
+		fmt.Printf(tableFmt, i, l)
+	}
+}