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.

Solution:

public int uniquePathsWithObstacles(int[][] obstacleGrid) { int width = obstacleGrid[0].length; int[] a = new int[width]; a[0] = 1; for (int[] row : obstacleGrid) { for (int j = 0; j < width; j++) { if (row[j] == 1) a[j] = 0; else if (j > 0) a[j] += a[j - 1]; } } return a[width - 1]; }