168. Excel Sheet Column Title (Math)

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

class Solution {
public:
    string convertToTitle(int n) {
        //residue is the value of current bit (from least-significant bit)
        //divided by 26, then iterate
        int residue = n%26, quotient=n;
        string ret = "";

        while(quotient>0){
            if(residue==0) {
                residue = 26; 
                quotient -= 1;
            }
            ret = (char)('A'+residue-1) + ret;
            
            quotient /= 26;
            residue = quotient %26;
        }
        
        return ret;
    }
};