63 Unique Paths II

Follow up for "Unique Paths":

Now consider if some obstacles are added to the grids. How many unique paths would there be?

An obstacle and empty space is marked as 1 and 0 respectively in the grid.

For example,

There is one obstacle in the middle of a 3x3 grid as illustrated below.

[  [0,0,0],  [0,1,0],  [0,0,0]]

The total number of unique paths is 2

public static int UniquePathsIIDP(List<List<int>> obstacleGrid)

        {

            int m = obstacleGrid.Count;

            int n = obstacleGrid[0].Count;

            int[,] grid = new int[m, n];

            // if the start point is a obstacle, return 0

            if (obstacleGrid[0][0] == 1)

                return 0;

            grid[0, 0] = 1;

            for (int i = 1; i < m; i++)

            {

                if (obstacleGrid[i][0] == 0 && grid[i - 1, 0] != 0)

                    grid[i, 0] = 1;

                else

                    grid[i, 0] = 0;

            }

            for (int i = 1; i < n; i++)

            {

                if (obstacleGrid[0][i] == 0 && grid[0, i - 1] != 0)

                    grid[0, i] = 1;

                else

                    grid[0, i] = 0;

            }

            for (int i = 1; i < m; i++)

            {

                for (int j = 1; j < n; j++)

                {

                    if (obstacleGrid[i][j] == 1)

                        grid[i, j] = 0;

                    else

                        grid[i, j] = grid[i - 1, j] + grid[i, j - 1];

                }

            }

            return grid[m - 1, n - 1];

        }