X is a good number 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. 0, 1, and 8 rotate to themselves; 2 and 5 rotate to each other; 6 and 9 rotate to each other, and the rest of the numbers do not rotate to any other number and become invalid.
Now given a positive number N, how many numbers X from 1 to N are good?
Example:
Input: 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.
Note:
- N will be in range
[1, 10000].
这道题定义了一种好数字，就是把每位上的数字自身翻转一下，能得到一个不同的数字。翻转规则定义为，0，1，和8翻转后还为其本身，2和5，6和9可以互相翻转。然后给了一个数字N，问 [1, N] 区间内共有多少个这样的好数字。这道题大家踩