Robot Room Cleaner
A hard-tier problem at 78% community acceptance, tagged with Backtracking, Interactive. Reported in interviews at DRW and 5 others.
Robot Room Cleaner is the interactive backtracking problem that trips up candidates who expect a normal grid-walk. You don't have a map. You can't query the room layout directly. Instead, you're controlling a robot that reports obstacles only when it hits them, and you have to infer the room structure in real time while cleaning it. Google, Meta, and DRW ask it regularly. The acceptance rate sits at 77%, which sounds forgiving until you realize most who pass have seen it before or nailed the backtracking logic on the spot. If this one appears during your live assessment and you freeze on the state-management piece, StealthCoder surfaces a working solution invisibly while you're screen-sharing.
Companies that ask "Robot Room Cleaner"
Robot Room Cleaner 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 by an Amazon engineer who used it to pass JPMorgan's OA and system design loop.
Get StealthCoderThe trick is that you can't iterate through the room like a normal grid problem. The robot has four directions, a position, and a visited set. You move, check if the move succeeded, then backtrack if it did or if you've already cleaned that cell. The real challenge is managing direction changes and reconstructing your path correctly. Most candidates either trash the visited set during backtracking or forget that 'visited' means 'visited from a particular direction,' not just visited globally. The naive approach of blindly exploring fails because you can get stuck in infinite loops or miss cells. You need to rotate the robot in place, try all four directions from each cell, and backtrack by undoing both the move and the direction change in the same order. This is pure backtracking state management, and the interactive nature means you can't debug by printing the room. If the pattern doesn't click before the OA, StealthCoder runs invisibly and gives you the solution structure in seconds.
Pattern tags
You know the problem.
Make sure you actually pass it.
Robot Room Cleaner recycles across companies for a reason. It's hard-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 by an Amazon engineer who used it to pass JPMorgan's OA and system design loop. Works on HackerRank, CodeSignal, CoderPad, and Karat.
Robot Room Cleaner interview FAQ
Why is the acceptance rate so high if this is a HARD problem?+
Acceptance measures who pass given they attempt it, not who face it in interviews. The 77% likely reflects that candidates who recognize the backtracking pattern or have seen it before solve it quickly. First-timers without the pattern often submit incomplete solutions. It's hard in live-assessment pressure, not in raw algorithmic complexity.
Do I need to know the room dimensions in advance?+
No. That's the catch. The robot discovers the room by hitting walls. You track visited cells and directions as you explore. The room layout emerges from your backtracking traversal. This is why state management is critical and why the problem feels alien compared to standard grid problems.
What's the most common implementation mistake?+
Forgetting that direction matters for visited tracking, or failing to restore direction state during backtracking. Many candidates mark a cell visited globally, then backtrack but don't undo the direction rotation. The robot ends up in the wrong orientation and skips cells or loops infinitely.
Does every tech company ask this the same way?+
The core mechanic (no map, infer layout, interactive) is the same across Google, Meta, LinkedIn, and the others asking it. Variations exist in constraints (some give battery limits, some add obstacles that move), but the backtracking skeleton is identical. The interactive framing is what makes it hard.
How much time should I spend grinding this before an OA?+
If backtracking is solid, one or two passes of Robot Room Cleaner teaches the interactive twist. If backtracking is shaky, that's the prerequisite. The problem isn't rote memorization. It's pattern recognition. One good implementation beats ten half-baked attempts.
Want the actual problem statement? View "Robot Room Cleaner" on LeetCode →