Paths Around the Walls — Solution & Editorial
dp[i][j] = dp[i−1][j] + dp[i][j−1] unless the cell is a wall (then 0); one row suffices in memory.
Complexity: O(NM)
dp[i][j] = dp[i−1][j] + dp[i][j−1] unless the cell is a wall (then 0); one row suffices in memory.
Complexity: O(NM)