Escape a Large Maze

Determine if you can reach target from source on a 10^6×10^6 grid with at most 200 blocked cells — the key challenge is that the blocked cells can form a small enclosed region despite the huge grid, so you must detect enclosure rather than search the whole grid. The typical approach is a bounded BFS/DFS from both source and target limited by the maximum area those blocked cells can enclose (≈O(N^2) with N≤200) to decide reachability.