##### ###### ##### ### # # ### # # ###### ## ## ## ## ## ## ## # # # # # ## ##### #### ##### # # # # # # # #### ## # ## ## ## ## # # # # # ## ## # ###### ## ### # ### # ######
##### ###### ##### ### # # ### # # ###### ## ## ## ## ## ## ## # # # # # ## ##### #### ##### # # # # # # # #### ## # ## ## ## ## # # # # # ## ## # ###### ## ### # ### # ######
(Setting blocked cells to 0)
If a cell has an obstacle, the number of paths through that cell is 0. You cannot reach it or pass through it.
Critical: If the starting cell or ending cell has an obstacle, return 0 immediately. No paths exist.
For other cells: if obstacle, set . Otherwise, use the same formula: .
