Convert Number to Excel Column

Problem

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

For example:

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

Examples

convertToTitle(27)
// returns "AA"
// 27 translates to "AA".

convertToTitle(52)
// returns "AZ"
// 52 corresponds to "AZ".

convertToTitle(705)
// returns "AAC"
// 705 spells out "AAC".