Cynthia digital root

src/main/java/org/fundacionjala/coding/cynthia/DigitalRoot.java

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+package org.fundacionjala.coding.cynthia;
+
+/**
+ * In this kata, you must create a digital root function.
+ * <p>
+ * A digital root is the recursive sum of all the digits in a number.
+ * Given n, take the sum of the digits of n. If that value has two digits,
+ * continue reducing in this way until a single-digit number is produced.
+ * This is only applicable to the natural numbers.
+ * <p>
+ * Here's how it works (Ruby example given):
+ * <p>
+ * sumOfDigits(16)
+ * => 1 + 6
+ * => 7
+ * <p>
+ * sumOfDigits(942)
+ * => 9 + 4 + 2
+ * => 15 ...
+ * => 1 + 5
+ * => 6
+ * <p>
+ * sumOfDigits(132189)
+ * => 1 + 3 + 2 + 1 + 8 + 9
+ * => 24 ...
+ * => 2 + 4
+ * => 6
+ * <p>
+ * sumOfDigits(493193)
+ * => 4 + 9 + 3 + 1 + 9 + 3
+ * => 29 ...
+ * => 2 + 9
+ * => 11 ...
+ * => 1 + 1
+ * => 2
+ */
+
+public class DigitalRoot {
+
+    /**
+     * @param num with the digits.
+     * @return the sum of digits.
+     */
+    public int sumOfDigits(int num) {
+        int res = 0;
+        while (num != 0) {
+            res += num % 10;
+            num = num / 10;
+        }
+        return res >= 10 ? sumOfDigits(res) : res;
+    }
+}

src/test/java/org/fundacionjala/coding/cynthia/DigitalRootTest.java

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+package org.fundacionjala.coding.cynthia;
+
+import static org.junit.Assert.assertEquals;
+
+import org.junit.Test;
+
+/**
+ * Created by Cynthia on 9/11/2017.
+ */
+public class DigitalRootTest {
+
+    /**
+     *
+     */
+    @Test
+    public void tests() {
+        DigitalRoot digital = new DigitalRoot();
+        assertEquals(7, digital.sumOfDigits(16));
+        assertEquals(6, digital.sumOfDigits(942));
+        assertEquals(6, digital.sumOfDigits(132189));
+        assertEquals(2, digital.sumOfDigits(493193));
+        assertEquals(9, digital.sumOfDigits(54));
+        assertEquals(1, digital.sumOfDigits(100));
+    }
+}