Given a positive integer, return its corresponding column title as appear in an Excel sheet.
For example:
    1 -> A
    2 -> B
    3 -> C
    ...
    26 -> Z
    27 -> AA
    28 -> AB 
    ...
Example 1:
Input: 1
Output: "A"
Example 2:
Input: 28
Output: "AB"
Example 3:
Input: 701
Output: "ZY"
class Solution:
     def convertToTitle(self, n):
         """
         :type n: int
         :rtype: str
         """
         letters = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'
         result = ''
         while n:
             n -= 1
             result = letters[n % 26] + result
             n //= 26
         
         return result
class Solution:
     def convertToTitle(self, n):
         """
         :type n: int
         :rtype: str
         """
         letters = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'
         result = ''
         while n:
             n -= 1
             result = letters[n % 26] + result
             n //= 26
         
         return result