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 class Solution {
    public int uniquePathsWithObstacles(int[][] obstacleGrid) {
        if (obstacleGrid == null || obstacleGrid.length == 0 || obstacleGrid[0].length == 0) {
            return 0;
        }
        
        int n = obstacleGrid.length;
        int m = obstacleGrid[0].length;
        int[][] paths = new int[n][m];
        
        for (int i = 0; i < n; i++) {
            if (obstacleGrid[i][0] != 1) {
                paths[i][0] = 1;
            } else {
                break;
            }
        }
        
        for (int i = 0; i < m; i++) {
            if (obstacleGrid[0][i] != 1) {
                paths[0][i] = 1; 
            } else {
                break;
            }
        }
        
        for (int i = 1; i < n; i++) {
            for (int j = 1; j < m; j++) {
                if (obstacleGrid[i][j] != 1) {
                    paths[i][j] = paths[i - 1][j] + paths[i][j - 1];
                } else {
                    paths[i][j] = 0;
                }
            }
        }
        
        return paths[n - 1][m - 1];
    }
}
class Solution {
    public int uniquePathsWithObstacles(int[][] obstacleGrid) {
        int[][] count = new int[obstacleGrid.length][obstacleGrid[0].length];
        if (obstacleGrid[0][0] == 0) 
            count[0][0] = 1;
        else 
            return 0;
        for (int i = 1; i < obstacleGrid[0].length; i++) {
            if (obstacleGrid[0][i] == 1) {
                count[0][i] = 0;
            } else {
                count[0][i] = count[0][i-1];
            }
        }
        
        for (int i = 1; i < obstacleGrid.length; i++) {
            if (obstacleGrid[i][0] == 1) {
                count[i][0] = 0;
            } else {
                count[i][0] = count[i-1][0];
            }
        }
        
        for (int i = 1; i < obstacleGrid.length; i++) {
            for (int j = 1; j < obstacleGrid[0].length; j++) {
                if (obstacleGrid[i][j] == 1) 
                    count[i][j] = 0;
                else
                    count[i][j] = count[i-1][j] + count[i][j-1];
            }
        }
        return count[obstacleGrid.length-1][obstacleGrid[0].length -1];
    }
}
class Solution {
    public int uniquePathsWithObstacles(int[][] obstacleGrid) {
        int m = obstacleGrid.length;
        int n = obstacleGrid[0].length;
        int[][] dp = new int[m+1][n+1];
        for (int i=1;i<m+1;i++){            
            if (obstacleGrid[i-1][0] == 1){
                break;
            }
            dp[i][1] = 1;
        }
        for (int i=1;i<n+1;i++){
            if (obstacleGrid[0][i-1] == 1){
                break;
            }
            dp[1][i] = 1;
        }
        for (int i=2;i<m+1;i++){
            for (int j=2; j<n+1; j++){
                if (obstacleGrid[i-1][j-1] != 1){
                    dp[i][j] = dp[i-1][j] + dp[i][j-1];
                }
            }
        }
        return dp[m][n];
    }
}