LeetCode:Unique Paths II

Unique Paths II

Total Accepted: 68571 Total
Submissions: 231545 Difficulty: Medium

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.

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 (M) Unique Paths

思路：

动规，有障碍的位置置0。

java code:

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

if(obstacleGrid == null || obstacleGrid.length == 0) return 0;
int rows = obstacleGrid.length;
int cols = obstacleGrid[0].length;

int[][] dp = new int[rows][cols];
if(obstacleGrid[0][0] == 0) dp[0][0] = 1;
for(int i = 1; i<rows; i++) {
if(obstacleGrid[i][0] == 0 && dp[i-1][0] == 1)
dp[i][0] = 1;
else
dp[i][0] = 0;
}
for(int i = 1; i<cols; i++) {

if(obstacleGrid[0][i] == 0 && dp[0][i-1] == 1)
dp[0][i] = 1;
else
dp[0][i] = 0;
}

for(int i=1;i<rows;i++) {
for(int j=1;j<cols;j++) {
if(obstacleGrid[i][j] == 1)
dp[i][j] = 0;
else
dp[i][j] = dp[i-1][j] + dp[i][j-1];
}
}
return dp[rows-1][cols-1];
}
}