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.

Analysis

link:https://leetcode.com/problems/unique-paths-ii/discuss/23373/Simple-Java-DP-solution

Solution from Forum (neat)

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