[leetcode]Excel Sheet Column Title

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

class Solution {
public:
    string convertToTitle(int n) {
        if(n<1) return "";
        string s,str;
        while(n){
           if(n%26==0){ 
           s.insert(0,"Z");
           n=n/26-1;
           }

           else{ 
           str='A'-1+n%26;
           s.insert(0,str);
           n/=26;
           }
        }
        return s;
    }
};