Add_Digits.md

258. Add Digits

Given a non-negative integer num, repeatedly add all its digits until the result has only one digit.

For example:

Given num = 38, the process is like: 3 + 8 = 11, 1 + 1 = 2. Since 2 has only one digit, return it.

Follow up:

• Could you do it without any loop/recursion in O(1) runtime?

Method:

recursion:

class Solution(object):
    def addDigits(self, num):
        """
        :type num: int
        :rtype: int
        """
        if num<10:
            return num
        return self.addDigits(num%10+self.addDigits(num/10))

or:

class Solution(object):
    def addDigits(self, num):
        """
        :type num: int
        :rtype: int
        """
        if num<10:
            return num
        return self.addDigits(num%10+num/10)

iteration:

class Solution(object):
    def addDigits(self, num):
        """
        :type num: int
        :rtype: int
        """
        while num>=10:
            tmp=0
            while num:
                tmp+=num%10
                num/=10
            num=tmp
        return num

Solution:

class Solution(object):
    def addDigits(self, num):
        """
        :type num: int
        :rtype: int
        """
        if not num:
            return 0
        return (num-1)%9+1