Excel Sheet Column Title

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 

方法：注意是n-1操作。

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