Description
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
DP
class Solution {
public int uniquePathsWithObstacles(int[][] obstacleGrid) {
if (obstacleGrid == null || obstacleGrid.length == 0
|| obstacleGrid[0].length == 0) {
return 0;
}
int m = obstacleGrid.length;
int n = obstacleGrid[0].length;
if (obstacleGrid[0][0] == 1 || obstacleGrid[m - 1][n - 1] == 1) {
return 0;
}
int[][] path = new int[m][n];
path[0][0] = 1;
for (int i = 0; i < m; ++i) {
for (int j = 0; j < n; ++j) {
if (obstacleGrid[i][j] != 0) {
path[i][j] = 0;
} else {
if (i > 0) path[i][j] += path[i - 1][j];
if (j > 0) path[i][j] += path[i][j - 1];
}
}
}
return path[m - 1][n - 1];
}
}
