Question

link

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.

Stats

Frequency 3
Difficulty 3
Adjusted Difficulty 2
Time to use --------

Ratings/Color = 1(white) 2(lime) 3(yellow) 4/5(red)

Solution

This is similar question as previous one, but DP solution.

My code

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