class Solution {public:    int uniquePathsWithObstacles(vector<vector<int> > &obstacleGrid) {        if(obstacleGrid[0][0]==1)            return 0;        int m=obstacleGrid.size();        int n=obstacleGrid[0].size();        int * row1=new int[n];        int * row2=new int[n];        row1[0]=obstacleGrid[0][0]==1?0:1;        int obs=0;//indicate the first row is obscaled        for(int i=1;i<n;i++)        {            if(row1[i-1]==0||obstacleGrid[0][i]==1)                row1[i]=0;            else                row1[i]=1;        }        for(int i=1;i<m;i++)        {            row2[0]=obstacleGrid[i][0]==1?0:1;            if(obstacleGrid[i][0]==1||obs==1)            {                obs=1;                row2[0]=0;            }            for(int j=1;j<n;j++)            {                if(obstacleGrid[i][j]==1)                    row2[j]=0;                else                {                    row2[j]=row2[j-1]+row1[j];                }            }            row1=row2;        }        return row1[n-1];    }};