LeetCode Js-258. Add Digits

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

給予一個整數 num，重複相加所有的數字直到結果只有個位數，並回傳該值。

ex. Input: nums = 18
18 = 1 + 8 --> 9
return 9

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.

Solution:

1. 如果 num 介於 0 ~ 9 之間，回傳 num。

2. 當 (num > 9)時宣告 sum = 0，且

3. 當 (num 的整數不等於 0)，
   執行以下：
   (1.) sum = 0 + 個位數
   (2.) num = num / 10

   將 num = sum，回傳 num。

Code:

var addDigits = function(num) {
  if (num < 10 && num >= 0) return num

  while (num > 9) {
    let sum = 0
    while (parseInt(num) !== 0) {
      sum += parseInt(num % 10)
      num /= 10
    }
    num = sum
  }
  return num
};

FlowChart:
Example 1

Input: num = 38

38 !== 0
--> 3 + 8 --> 11

11 !== 0
--> 1 + 1 --> 2 

2 < 9, return 2