#788
Rotated Digits
medium · verified · 56.8% accepted · 785 likes · top 52%
Description
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].
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
Solution