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 as1and0respectively in the grid.

Notice

mandnwill be at most 100.

Example

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 is2.

这题跟上一题62的不同在于这里有obstacle。除了obstacle的位置要设成0以为，跟上一题一样。

public int uniquePathsWithObstacles(int[][] obstacleGrid) {
    if (obstacleGrid == null || obstacleGrid.length == 0 || obstacleGrid[0].length == 0 ) {
        return 0;
    }

    int[][] dp = new int[obstacleGrid.length][obstacleGrid[0].length];
    //init 1st col
    for (int i = 0; i < obstacleGrid.length; i++) {
        if (obstacleGrid[i][0] == 1 || (i > 0 && dp[i - 1][0] == 0)) {
            dp[i][0] = 0;
        } else {
            dp[i][0] = 1;
        }
    }

    //init 1st row
    for (int j = 0; j < obstacleGrid[0].length; j++) {
        if (obstacleGrid[0][j] == 1 || (j > 0 && dp[0][j - 1] == 0)) {
            dp[0][j] = 0;
        } else {
            dp[0][j] = 1;
        }
    }

    //fill the dp matrix
    for (int i = 1; i < obstacleGrid.length; i++) {
        for (int j = 1; j < obstacleGrid[0].length; j++) {
            if (obstacleGrid[i][j] == 1) {
                dp[i][j] = 0;
            } else {
                dp[i][j] = dp[i - 1][j] + dp[i][j - 1];
            }
        }
    }

    return dp[obstacleGrid.length - 1][obstacleGrid[0].length - 1];
}