Given two positive integers a and b, return the number of common factors of a and b.
An integer x is a common factor of a and b if x divides both a and b.
Example 1:
Input: a = 12, b = 6 Output: 4 Explanation: The common factors of 12 and 6 are 1, 2, 3, 6.
Example 2:
Input: a = 25, b = 30 Output: 2 Explanation: The common factors of 25 and 30 are 1, 5.
Constraints:
1 <= a, b <= 1000