Validate Pin

Create a function to test if a string is a valid pin or not.

A valid pin has:

• Exactly 4 or 6 characters.
• Only numerical characters (0-9).
• No whitespace.

Examples

valid("1234") ➞ True

valid("45135") ➞ False

valid("89abc1") ➞ False

valid("900876") ➞ True

valid(" 4983") ➞ False

Notes

Empty strings should return False when tested.