0788. Rotated Digits

https://leetcode.com/problems/rotated-digits

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

Constraints:

• 1 <= n <= 104

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