Max Difference You Can Get From Changing an Integer

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

Pick a digit x (0 <= x <= 9).
Pick another digit y (0 <= y <= 9). The digit y can be equal to x.
Replace all the occurrences of x in the decimal representation of num by y.
The new integer cannot have any leading zeros, also the new integer cannot be 0.

Let a and b be the results of applying the operations to num the first and second times, respectively.

Return the max difference between a and b.

Example 1:

Input: num = 555
Output: 888
Explanation: The first time pick x = 5 and y = 9 and store the new integer in a.
The second time pick x = 5 and y = 1 and store the new integer in b.
We have now a = 999 and b = 111 and max difference = 888

Example 2:

Input: num = 9
Output: 8
Explanation: The first time pick x = 9 and y = 9 and store the new integer in a.
The second time pick x = 9 and y = 1 and store the new integer in b.
We have now a = 9 and b = 1 and max difference = 8

Example 3:

Input: num = 123456
Output: 820000

Example 4:

Input: num = 10000
Output: 80000

Example 5:

Input: num = 9288
Output: 8700

Solution:

class Solution {
    public int maxDiff(int num) {
        String s = String.valueOf(num);
        String min = s;
        if (s.charAt(0) != '1') {
            min = s.replaceAll(Character.toString(s.charAt(0)), "1");
        } else {
            for (int i = 1; i < s.length(); i ++) {
                if (s.charAt(i) != '0' && s.charAt(0) != s.charAt(i)) {
                    min = s.replaceAll(Character.toString(s.charAt(i)), "0");
                    break;
                }
            }
        }
        String max = s;
        if (s.charAt(0) != '9') {
            max = s.replaceAll(Character.toString(s.charAt(0)), "9");
        } else {
            for (int i = 1; i < s.length(); i ++) {
                if (s.charAt(i) != '9' && s.charAt(0) != s.charAt(i)) {
                    max = s.replaceAll(Character.toString(s.charAt(i)), "9");
                    break;
                }
            }
        }
        // System.out.println(max + ", " + min);
        return Integer.parseInt(max) - Integer.parseInt(min);
    }
}