We can rotate digits by 180 degrees to form new digits. When 0, 1, 6, 8, 9 are rotated 180 degrees, they become 0, 1, 9, 8, 6 respectively. When 2, 3, 4, 5 and 7 are rotated 180 degrees, they become invalid.
A confusing number is a number that when rotated 180 degrees becomes a different number with each digit valid.(Note that the rotated number can be greater than the original number.)
Given a positive integer N, return the number of confusing numbers between
1 and N inclusive.
Example 1:
Input: 20 Output: 6 Explanation: The confusing numbers are [6,9,10,16,18,19]. 6 converts to 9. 9 converts to 6. 10 converts to 01 which is just 1. 16 converts to 91. 18 converts to 81. 19 converts to 61.
Example 2:
Input: 100 Output: 19 Explanation: The confusing numbers are [6,9,10,16,18,19,60,61,66,68,80,81,86,89,90,91,98,99,100].
Note:
1 <= N <= 10^9