[leetcode 168] 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

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