[Leetcode] 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.

Easy DP problem, pay attention to the initial state, I make a mistake on that the first time writing the code.

    public int uniquePathsWithObstacles(int[][] obstacleGrid) {
        int m = obstacleGrid.length;
        if(m == 0) return 0;
        int n = obstacleGrid[0].length;
        if(n == 0) return 0;
        int[] dp = new int[n];
        for(int i = 0; i < n; i++) {
            if(obstacleGrid[0][i] == 1)
                dp[i] = 0;
            else 
                dp[i] = (i == 0 ? 1 : dp[i-1]);
        }
        for(int i = 1; i < m; i++) {
            for(int j = 0; j < n; j++) {
                if(obstacleGrid[i][j] == 1)
                    dp[j] = 0;
                else
                    dp[j] = dp[j] + (j == 0 ? 0 : dp[j-1]);
            }
        }
        return dp[n-1];
    }