[LeetCode] 258. Add Digits

258.py

class Solution(object):
    def addDigits_recursion(self, num):
        """
        :type num: int
        :rtype: int
        """
        num_str = str(num)
        if len(num_str) == 1:
            return num
        new_num = 0
        for s in num_str:
            new_num += int(s)
        return self.addDigits_recursion(new_num)
        
    def addDigits_loop(self, num):
        """
        :type num: int
        :rtype: int
        """
        num_str = str(num)
        while len(num_str) != 1:
            new_num = 0
            for s in num_str:
                new_num += int(s)
            num_str = str(new_num)
        return int(num_str)
    
    # 自行 Google -> 数根 Digits Root
    def addDigits_formula(num):
        if num / 9 == 0:
              return num
        if num % 9 == 0:
            return 9
        return num % 9