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 

public class Solution {
    public string ConvertToTitle(int n) {
        var sb = new StringBuilder();
        
        while (n > 0)
        {
            var up = (n - 1) / 26;
            var left = (n - 1) % 26;
            
            sb.Insert(0, (char)(left + (int)'A'));
            n = up;
        }
        
        return sb.ToString();
    }
}