add-digits.js

/*
Given an integer num, repeatedly add all its digits until the result has only one digit, and return it.

 

Example 1:

Input: num = 38
Output: 2
Explanation: The process is
38 --> 3 + 8 --> 11
11 --> 1 + 1 --> 2 
Since 2 has only one digit, return it.
Example 2:

Input: num = 0
Output: 0
 

Constraints:

0 <= num <= 231 - 1
 

Follow up: Could you do it without any loop/recursion in O(1) runtime?
*/

/**
 * @param {number} num
 * @return {number}
 */
var addDigits = function(num) {

    while (num.toString().length > 1){
        let holder = 0
        console.log(num.toString().split('').length)
        for (let i = 0; i < num.toString().split('').length; i++){
            holder += num.toString().split('')[i] * 1
        }
        num = holder
        console.log(num)
    } 

    return num
};