Given two positive integers a and b, return the count of numbers having unique digits in the range [a, b] (inclusive).

 

Example 1:

Input: a = 1, b = 20
Output: 19
Explanation: All the numbers in the range [1, 20] have unique digits except 11. Hence, the answer is 19.

Example 2:

Input: a = 9, b = 19
Output: 10
Explanation: All the numbers in the range [9, 19] have unique digits except 11. Hence, the answer is 10. 

Example 3:

Input: a = 80, b = 120
Output: 27
Explanation: There are 41 numbers in the range [80, 120], 27 of which have unique digits.

 

Constraints:

• 1 <= a <= b <= 1000