This was the difficult question I remember they asked. It's a variant of this question. Leetcode 489. Robot Room Cleaner Control a robot with only move/turn/clean APIs to traverse and clean every reachable cell in an unknown grid with obstacles and no global map. The challenge is to explore the entire accessible area using DFS/backtracking while tracking visited coordinates and managing orientation to avoid revisiting or getting stuck. DESCRIPTION Control a robot with only move/turn/clean APIs to traverse and clean every reachable cell in an unknown grid with obstacles and no global map. The challenge is to explore the entire accessible area using DFS/backtracking while tracking visited coordinates and managing orientation to avoid revisiting or getting stuck. Input: room = [ [1,1,1,1,1,0,1,1], [1,1,1,1,1,0,1,1], [1,0,1,1,1,1,1,1], [0,0,0,1,0,0,0,0], [1,1,1,1,1,1,1,1] ], row = 1, col = 3 Output: Robot cleans all reachable cells Explanation: The robot starts at position (1,3) and explores the entire reachable area using DFS with backtracking. Cells with 0 are obstacles, cells with 1 are cleanable. Constraints: 1 <= room.length <= 100 1 <= room[i].length <= 200 room[i][j] is either 0 (obstacle) or 1 (cleanable) The robot starts in a cleanable cell All cleanable cells are connected (reachable from the starting position) Robot APIs: move() returns boolean, turnLeft() and clean() return void