You are given an integer num. You will apply the following operation exactly two times:

1. Select a digit x ($0 \leq x \leq 9$) and a digit y ($0 \leq y \leq 9$). The digit y can be equal to x.

2. Replace every occurrence of x in the decimal representation of num with y.

3. The resulting integer cannot have leading zeros and cannot be equal to $0$.

Let a and b be the integers obtained from the first and second operations, respectively.

Return the maximum possible value of a $-$ b.

Constraints:

• $1 \leq$ num $\leq 10^8$

Now, let’s take a moment to make sure you’ve correctly understood the problem. The quiz below helps you check if you’re solving the correct problem:

We have a game for you to play. Rearrange the logical building blocks to develop a clearer understanding of how to solve this problem.

Implement your solution in the following coding playground.