leetcode 504. Base 7

class Solution(object):
    def convertToBase7(self, num):
        """
        :type num: int
        :rtype: str
        """
        """
        Input: 100
Output: "202"
100%7=14,2
14%7=2,0
2%7=2,xxx
        """
        is_neg = False
        if num < 0:            
            num = -num
            is_neg = True
        ans = ""
        while num >= 7:
            ans = str(num%7) + ans
            num = num/7
        ans = str(num) + ans
        return ans if not is_neg else "-"+ans

class Solution(object):
    def convertToBase7(self, num):
        """
        :type num: int
        :rtype: str
        """
        """
        Input: 100
Output: "202"
100%7=14,2
14%7=2,0
2%7=2,xxx
        """
        if num == 0:
            return '0'
        is_neg = False
        if num < 0:            
            num = -num
            is_neg = True        
        ans = ""
        while num != 0:
            ans = str(num%7) + ans
            num = num/7        
        return ans if not is_neg else "-"+ans

class Solution(object):
    def convertToBase7(self, num):
        """
        :type num: int
        :rtype: str
        """
        if num < 0:
            return "-"+self.convertToBase7(-num)
        if num < 7:
            return str(num)
        return self.convertToBase7(num/7) + str(num%7)