788. Rotated Digits

Difficulty: Medium

Topics: Senior , Math , Dynamic Programming , Weekly Contest 73

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

Example…