Implement LC 258 Add Digits

Author: timothyshores

258. Add Digits.js

@@ -23,8 +23,10 @@ Follow up: Could you do it without any loop/recursion in O(1) runtime?
 
 */
 
+const sumDigitsFromNum = (num) => [...num.toString()].map((num) => Number(num)).reduce((a, b) => a + b, 0);
+
 /**
  * @param {number} num
  * @return {number}
  */
-const addDigits = (num) => {};
+const addDigits = (num) => (num < 10 ? num : addDigits(sumDigitsFromNum(num)));

README.md

@@ -30,6 +30,7 @@ LeetCode Profile: https://leetcode.com/timothyshores/
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 |[242. Valid Anagram](https://leetcode.com/problems/valid-anagram/)|Easy|[JavaScript](242.%20Valid%20Anagram.js)
+|[258. Add Digits.js](https://leetcode.com/problems/add-digits/)|Easy|[JavaScript](258.%20Add%20Digits.js)
 |[278. First Bad Version](https://leetcode.com/problems/first-bad-version/)|Easy|[JavaScript](278.%20First%20Bad%20Version.js)
 |[283. Move Zeroes](https://leetcode.com/problems/move-zeroes/)|Easy|[JavaScript](283.%20Move%20Zeroes.js)
 |[287. Find the Duplicate Number](https://leetcode.com/problems/find-the-duplicate-number/)|Medium|[JavaScript](287.%20Find%20the%20Duplicate%20Number.js)