168. Excel Sheet Column Title

Given an integer columnNumber, return _its corresponding column title as it appears in an Excel sheet.

For example:

A -> 1
B -> 2
C -> 3
...
Z -> 26
AA -> 27
AB -> 28
...

Example 1:

Input: columnNumber = 1
Output: "A"

Example 2:

Input: columnNumber = 28
Output: "AB"

Example 3:

Input: columnNumber = 701
Output: "ZY"

def convertToTitle(self, columnNumber: int) -> str:
	res = ''
	while columnNumber > 26:
		r = columnNumber % 26
		columnNumber = columnNumber // 26
		if r == 0:
			r = 26
			columnNumber -= 1
		res = (chr(r+64)) + res
	res = chr(columnNumber + 64) + res
	return res