[LeetCode]168 Excel Sheet Column Title

public class Solution {
public String convertToTitle(int n) {

if (n <= 0)
return null;

StringBuilder sb = new StringBuilder();
do
{
int d = n % 26;
sb.append(toC(d));
n = (n - 1) / 26;
}
while (n > 0);

return sb.reverse().toString();
}

private char toC(int d)
{
if (d == 0)
d = 26;
return (char)('A' + d - 1);
}
}