788. Rotated Digits-旋转数字

X is a good number if after rotating each digit individually by 180 degrees, we get a valid number that is different from X.  Each digit must be rotated – we cannot choose to leave it alone.

A number is valid if each digit remains a digit after rotation. 0, 1, and 8 rotate to themselves; 2 and 5 rotate to each other (on this case they are rotated in a different direction, in other words 2 or 5 gets mirrored); 6 and 9 rotate to each other, and the rest of the numbers do not rotate to any other number and become invalid.

Now given a positive number N, how many numbers X from 1 to N are good?

Example:
Input: 10
Output: 4
Explanation:
There are four good numbers in the range [1, 10] : 2, 5, 6, 9.
Note that 1 and 10 are not good numbers, since they remain unchanged after rotating.
Note:
N  will be in range [1, 10000].

Solution in python:

class Solution:
    def rotatedDigits(self, N: int) -> int:

        def isValid(num):
            aset = set([0, 1, 8, 2, 5, 6, 9])
            bset = set([2, 5, 6, 9])
            flag = False
            while num > 0:
                num, r = divmod(num, 10)
                if r not in aset:
                    return False
                if r in bset:
                    flag = True
            return flag

        result = 0 
        for i in range(1, N+1):
            if isValid(i):
                result += 1
        return result