Given an `n x n` binary grid, where `0` means open and `1` means blocked, return the length of the shortest clear path from the top-left cell to the bottom-right cell. You may move in all 8 directions to neighboring cells: horizontal, vertical, and diagonal. A valid path may only pass through open cells. Return `-1` if either endpoint is blocked or no path exists. ### Constraints & Assumptions - The path length counts the number of cells visited, including the start and end cells. - The grid is square: `n x n`. - Diagonal moves are allowed. - Mutating the grid for visited marking is acceptable if stated, but a separate visited set is also fine. - Use breadth-first search because all moves have equal cost. ### Clarifying Questions to Ask - Does path length count edges or cells? - Are diagonal moves allowed through corners if adjacent orthogonal cells are blocked? - Can I mutate the input grid? - What should be returned for an empty grid? ### What a Strong Answer Covers - Endpoint-blocked checks. - BFS from `(0, 0)`. - 8-direction neighbor generation. - Visited marking to avoid cycles. - First time reaching bottom-right gives shortest path. - Time and space complexity. ### Follow-up Questions - How would the solution change if moves had different costs? - How would you return the actual path, not only length? - How would you handle a rectangular grid? - How would you solve it if diagonal corner-cutting were disallowed?