leetcode 63. 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.

上题：

public int uniquePathsWithObstacles(int[][] obstacleGrid) {
int m = obstacleGrid.length;
if(m == 0) return 0;
int n = obstacleGrid[0].length;
int[][] dp = new int[m]
;
int i,j;
for(int index = m*n-1;index >= 0;index--){
i = index / n;
j = index % n;
if(obstacleGrid[i][j] == 1){
dp[i][j] = 0;
}
else if(index == m*n-1) dp[i][j] = 1;
else{
dp[i][j] = 0;
if(i+1 < m) dp[i][j] += dp[i+1][j];
if(j+1 < n) dp[i][j] += dp[i][j+1];
}

}
return dp[0][0];
}

加入一个逻辑即可：

if(obstacleGrid[i][j] == 1){
dp[i][j] = 0;
}