it-mapping approach in C++.
Key idea:
Use a mirror mapping for digits (0→0, 1→1, 2→5, 5→2, 6→9, 9→6)
Skip invalid digits (3, 4, 7)
Count numbers that become a different valid number after rotation
Approach:
Iterate from 2 to n
Extract digits and map them using a lookup array
Reject numbers containing invalid digits
Ensure at least one digit changes after rotation
Time Complexity: O(n * d), where d = number of digits
Space Complexity: O(1)
Code is simple, avoids string conversion, and uses pure arithmetic for speed.
#leetcode #cpp #algorithms #codinginterview #dsa #programming #competitiveprogramming #coding #datastructures #leetcodechallenge
