LeetCode Online Judge 题目C# 练习 - 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.

Note: m and n will be at most 100.

        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];
        }

代码分析：

　　这题用DP，超容易。