ABA Integers: the Undulating Numbers

In this challenge, you have to establish if a given number is undulating. A number n is undulating when the following conditions are all true:

• n has at least three digits.
• n has exactly two different digits.
• The two digits of n are alternating without repeating groups.

If we think at the first digit of an undulating number as an "A", and to its second digit as a "B", we can notice a sequence of the form "ABA", that can repeat infinite times and ends either with an "A" or with a "B", but without clusters of "AA" or "BB" into it.

Given a positive integer n, implement a function that returns true if n is an Undulating number, or false if it's not.

Examples

isUndulating(121) ➞ true
// A = 1, B = 2
// The sequence ABA is valid

isUndulating(373737) ➞ true
// A = 3, B = 7
// The sequence ABABABAB is valid

isUndulating(12) ➞ false
// Less than three digits

isUndulating(12122) ➞ false
// The sequence ABABB is not valid

isUndulating(85856) ➞ false
// More than two different digits

Notes

N/A