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 
    ...

Example 1:

Input: 1
Output: "A"

Example 2:

Input: 28
Output: "AB"

Example 3:

Input: 701
Output: "ZY"

string convertToTitle(int n) { // time: O(n); space: O(n)
    string res;
    char tmp;
    while (n != 0) {
        n -= 1;
        tmp = 'A' + (n % 26);
        res += tmp;
        n /= 26;
    }
    reverse(res.begin(), res.end());
    return res;
}