Grid 1 - Handling Walls

What if cell $(i,j)$ is a wall (#)? You can't stand on a wall, so no paths can reach it. Set $dp[i][j] = 0$ for any wall cell. Walls block paths completely.

When computing $dp[i][j]$ for a passable cell, treat each blocked neighbor as contributing $0$ paths. Since $0 + x = x$, the formula $dp[i][j] = dp[i-1][j] + dp[i][j-1]$ works unchanged. Initialize all wall cells to $0$ before running the DP.