Unique Paths II ——LeetCode

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.

跟上一个题类似。

题目大意：左上走到右下，1表示障碍，0表示路，问有多少种唯一的走法。

解题思路：简单的动规，F(i,j)=F(i-1,j)+F(i,j-1)，如果grid[i][j]==1，那么F(i,j)=0。

public class Solution {
    public int uniquePathsWithObstacles(int[][] og) {
        if(og==null||og[0].length==0||og[0][0]==1){
            return 0;
        }
        int m = og.length,n=og[0].length;
        int[][] cnt = new int[m][n];
        cnt[0][0]=1;
        for(int i=0;i<m;i++){
            for(int j=0;j<n;j++){
                if((i==0&&j==0)||og[i][j]==1){
                    continue;
                } else if(i==0&&j!=0){
                    cnt[i][j]=cnt[i][j-1];
                } else if(j==0&&i!=0){
                    cnt[i][j]=cnt[i-1][j];
                } else {
                    cnt[i][j]=cnt[i-1][j]+cnt[i][j-1];
                }
            }
        }
        return cnt[m-1][n-1];
    }
}