Given an integer, return its base 7 string representation.

Example 1:

Input: 100

Output: "202"

Example 2:

Input: -7

Output: "-10"

Note: The input will be in range of [-1e7, 1e7].

class Solution(object):

    def convertToBase7(self, num):

        """

        :type num: int

        :rtype: str

        """

        ans=""

        if num<0:

            neg=True

        else:

            neg=False

        num=abs(num)

        while num>=7:

            ans+=str(num%7)

            num=num//7

        ans+=str(num)

        if neg:

            ans='-'+ans[::-1]

            return ans

        return ans[::-1]