LeetCode Js-258. Add Digits

    AllenLi
    LeetCode Js-Number

    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.

    Example 2:

    Input: num = 0
Output: 0

    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 1:

    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

    Example 2

    Input: num = 0

return 0

    Code 2:

    var addDigits = function(num) {
  if (num === 0) return 0;
  if (num % 9 === 0) return 9;
  return num % 9;
};

    Code 3:

    var addDigits = function(num) {
   return 1 + (num - 1) % 9
};

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