excel sheet column title

public String (int n) {
    if (n == 0)
        return "";
    StringBuilder sb = new StringBuilder();
    while (n != 0) {
        int offset = (n - 1) % 26;
        char c = (char)(offset + 'A');
        sb.insert(0, c);
        n = (n - 1) / 26;
    }
    return sb.toString();
}

public int titleToNumber(String s) {
    if (s == null || s.length() == 0)
        return 0;
    int ans = 0;
    for (int i = 0; i < s.length(); ++i) {
        char c = s.charAt(i);
        ans = ans * 26 + c - 'A' + 1;
    }
    return ans;
}