leetcode---Excel Sheet Column Title

Given a positive integer, return its corresponding column title as appear in an Excel sheet.

For example:

1 -> A2 -> B3 -> C...26 -> Z27 -> AA28 -> AB 

class Solution {public:    string convertToTitle(int n)     {        string s;        while(n)        {            int a = (n-1) % 26;            char c = 'A' + a;            s = c + s;            n = (n-1) / 26;        }        return s;    }};