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
Constraints:
1 <= num <= 10^8
class Solution:
    def maxDiff(self, num: int) -> int:
        if num < 10: return 8
        a = b = str(num)
        i = 0
        while i < len(a):
            if a[i] == '9':
                i += 1
            else:
                a = a.replace(a[i], '9')
                break

        if b[0] != '1':
            b = b.replace(b[0], '1')
        else:
            i = 1
            while i < len(b):
                if b[i] == '1' or b[i] == '0':
                    i += 1
                else:
                    b = b.replace(b[i], '0')
                    break
        #print(a,b)
        return int(a) - int(b)
class Solution:
    def maxDiff(self, num: int) -> int:
        if num < 10: return 8
        a = b = str(num)
        i = 0
        while i < len(a):
            if a[i] == '9':
                i += 1
            else:
                a = a.replace(a[i], '9')
                break

        if b[0] != '1':
            b = b.replace(b[0], '1')
        else:
            i = 1
            while i < len(b):
                if b[i] == '1' or b[i] == '0':
                    i += 1
                else:
                    b = b.replace(b[i], '0')
                    break
        #print(a,b)
        return int(a) - int(b)