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。