Rotated Digits
A medium-tier problem at 56% community acceptance, tagged with Math, Dynamic Programming. Reported in interviews at Arista Networks and 0 others.
Rotated Digits is a deceptively tricky problem that hits most candidates in the same spot: you understand what rotated digits are, you understand the goal, but halfway through coding you realize the brute force won't scale and you've missed the DP angle. It's asked at companies like Arista Networks and shows up in assessments where candidates have limited time to pivot. The acceptance rate sits at 56%, which means nearly half the people who attempt it don't pass. If this lands in your live OA and you blank on the state-space reduction, StealthCoder surfaces a working solution while the proctor sees nothing.
Companies that ask "Rotated Digits"
Rotated Digits is the kind of problem that decides whether you pass. StealthCoder reads the problem on screen and surfaces a working solution in under 2 seconds. Invisible to screen share. The proctor sees nothing. Built because the OA filter rejects engineers who'd pass the on-site. That's a broken filter. This is the workaround.
Get StealthCoderThe trick here is recognizing that you can't just iterate through a range and check each number individually when the range is large. Most people start with a naive digit-rotation check and a loop, only to hit timeout. The real solution uses dynamic programming to count valid rotated numbers by building up from smaller numbers to larger ones, exploiting the structure of digit rotation itself. The key insight is that certain digits (0, 1, 8) look the same when rotated, some digits (2, 5, 6, 9) map to each other, and others (3, 4, 7) can't be rotated at all. If a number contains any non-rotateable digit, it's invalid. DP lets you avoid checking every single number in the range. When you hit this problem cold in an assessment, the pivot from brute force to digit-DP happens too late. StealthCoder runs invisibly and gives you the DP structure in seconds.
Pattern tags
You know the problem.
Make sure you actually pass it.
Rotated Digits recycles across companies for a reason. It's medium-tier, and most candidates blank under the timer. StealthCoder is the hedge: an AI overlay invisible during screen share. It reads the problem and surfaces a working solution in under 2 seconds. Built because the OA filter rejects engineers who'd pass the on-site. That's a broken filter. This is the workaround. Works on HackerRank, CodeSignal, CoderPad, and Karat.
Rotated Digits interview FAQ
How hard is Rotated Digits really compared to other DP problems?+
It's medium difficulty and the acceptance rate of 56% reflects that. The hard part isn't the DP itself, it's recognizing you need DP at all. Once you see the digit-rotation rules and the state-building approach, the implementation is straightforward. Most failures happen because candidates try a brute-force loop first.
Is this still asked in live interviews or mostly OAs?+
It appears in online assessments more often than live whiteboard rounds. Arista Networks is on the list of companies that ask it. The nature of the problem (counting valid numbers in a range) fits assessment formats better than interactive interviews.
What's the core trick I need to remember?+
Digit rotation has fixed rules: some digits are invalid (3, 4, 7), some map to themselves (0, 1, 8), and some swap pairs (2-5, 6-9). Use DP to count valid numbers digit by digit instead of iterating the entire range. This avoids timeout on large ranges.
How does this problem connect to the Math and Dynamic Programming topics?+
The Math part is understanding digit rotation rules and properties. The DP part is the algorithm: build a count of valid numbers by placing digits one at a time and tracking whether the number is still a valid rotation. Both pieces are essential to solve it efficiently.
If I only memorize the solution, will it help in an assessment?+
Not as much as understanding the pattern. But if you freeze during your OA, memorizing the DP structure and the rotation rules is enough to ship working code. That's where StealthCoder comes in: a real-time reminder of the approach when your memory blanks.
Want the actual problem statement? View "Rotated Digits" on LeetCode →