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 
...

class Solution {
public:
    string convertToTitle(int columnNumber) {
        string res = "";
        while(columnNumber) {
            columnNumber -= 1;
            res.push_back((columnNumber % 26) + 'A');
            columnNumber /= 26;
        }
        reverse(begin(res),end(res));
        return res;
    }
};