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Yes, Robot Room Cleaner is considered a classic hard interview problem and has appeared in variations in FAANG-style interviews. It tests understanding of DFS, backtracking, coordinate simulation, and working with constrained APIs.
A hash set is typically used to store visited coordinates so the robot does not revisit the same cell. This allows efficient O(1) lookups while performing DFS exploration of the grid.
Backtracking allows the robot to return to its previous position after exploring a direction. Since the robot must maintain orientation and location to explore remaining paths, backtracking ensures systematic coverage of all reachable cells.
The optimal approach uses backtracking combined with depth-first search. By tracking visited cells and exploring all four directions recursively, the robot can clean every reachable space while returning to previous positions to continue exploration.