pad.go
func zfillInt(src int, z int) string {
	if z < 2 {
		return strconv.Itoa(src)
	}
	return fmt.Sprintf(fmt.Sprintf("%%0%dd", z), src)
}
func zfillInt(src int, z int) string {
	if z < 2 {
		return strconv.Itoa(src)
	}
	return fmt.Sprintf(fmt.Sprintf("%%0%dd", z), src)
}
// Left pads an int to a given with, using "0".
// If the string begins with a negative "-" character, then
// padding is inserted between the "-" and the remaining characters.