package UniquePathsII;

/**

* User: Danyang

* Date: 1/19/2015

* Time: 20:35

*

* 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 {

/**

* f[i][j] = f[i-1][j] + f[i][j-1] if possible

* Notice:

* 1. boundary case

* 2. it itself is obstacle

* @param obstacleGrid

* @return

*/

public int uniquePathsWithObstacles(int[][] obstacleGrid) {

int m = obstacleGrid.length;

if(m==0)

return 0;

int n = obstacleGrid[0].length;

if(n==0)

return 0;

int[][] f = new int[m+1][n+1];

f[0][1] = 1;

for(int i=1; i<m+1; i++)

for(int j=1; j<n+1; j++) {

if(i-2<0 || obstacleGrid[i-2][j-1]==0)

f[i][j] += f[i-1][j];

if(j-2<0 || obstacleGrid[i-1][j-2]==0)

f[i][j] += f[i][j-1];

if(obstacleGrid[i-1][j-1]==1)

f[i][j] = 0;

}

return f[m][n];

}

}