code: static private String zeros(int n)
    {
      if (n < 1)
        return "";
  
      char[] buf = new char[n];
  
      for (int i = 0; i < n; i++)
      {
        buf[i] = '0';
      }
  
      return new String(buf);
    }
docs: Return a string of '0' of the given length
  
  
  @param n Length of the string to be returned
  
  @return a string of '0' with the given length