题目描述：

LeetCode 788. Rotated Digits

X is a good number if after rotating each digit individually by 180 degrees, we get a valid number that is different from X. 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; 6 and 9 rotate to each other, and the rest of the numbers do not rotate to any other number.

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].

题目大意：

将数字翻转180度，0, 1, 8会保持原状, 2和5会互换，6和9会互换，其余数字无法翻转。

求1 ~ N中，所有数位均可以翻转，并且翻转后与原数字不同的数字的个数。

解题思路：

蛮力法（Brute Force）

Python代码：

class Solution(object):
    def rotatedDigits(self, N):
        """
        :type N: int
        :rtype: int
        """
        ans = 0
        for n in range(1, N + 1):
            nset = set(map(int, str(n)))
            if any(x in nset for x in (2, 5, 6, 9)):
                if not any(x in nset for x in (3, 4, 7)):
                    ans += 1
        return ans

 

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