added Find digital root of a number in Scala

program/program/find-digital-root-of-a-number/findDigitalRootOfANumber.scala

@@ -0,0 +1,20 @@
+import scala.annotation.tailrec
+
+object findDigitalRootOfANumber {
+  def main(args: Array[String]): Unit = {
+    val number = 942
+    println(digitalRoot(number))
+  }
+
+  def sumOfDigits(n: Int): Int = {
+    if (n == 0) 0
+    else n % 10 + sumOfDigits(n / 10)
+  }
+
+  @tailrec
+  def digitalRoot(n: Int): Int = {
+    val sum = sumOfDigits(n)
+    if (sum < 10) sum
+    else digitalRoot(sum)
+  }
+}