What I know is 9(a-b). No matter what the answer is, the sum of its ten digits and two numbers must be =9, and then calculate =18x-81(x =1-9). No matter what the result is, the number of digits must be odd, and the number of digits must be even (positive or negative).

9-27-63-8 1, (negative numbers can also get the same result) and these numbers can be converted into 45 no matter how they evolve, so you can draw your conclusion (only two digits)

As for those with more than three digits, I can't list them. I can only guess whether there is a three-digit number, assuming it is a middle number, and this middle number can be changed back to a two-digit number. Similarly, four digits will become three digits, and so on. In this way, we only need to prove that the intermediate number can be obtained after finite subtraction, then everything can be answered. This is my guess.