Rotated Digits

Problem Statement

An integer x is a good 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. For example:

• 0, 1, and 8 rotate to themselves,
• 2 and 5 rotate to each other (in 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.

Given an integer n, return the number of good integers in the range [1, n].

Leetcode link

Example 1:

Input: n = 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.

Example 2:

Input: n = 1
Output: 0

Example 3:

Input: n = 2
Output: 1

Constraints:

• 1 <= n <= 10⁴

Code

Python Code

class Solution(object):
    def rotatedDigits(self, N):
        def isValidRotation(num):
            return (not any(s in {'3', '4', '7'} for s in num)) and any(s in {'2', '5', '6', '9'} for s in num)

        return sum([isValidRotation(str(i)) for i in range(1, N+1)])