63. Unique Paths II

动态规划：

F[i][j]=F[i-1]+F[i][j-1](F[i][j]=0,when grid[i][j]==1)

class Solution {
public:
    int uniquePathsWithObstacles(vector<vector<int>>& grid) {
        int ans[100][100]={0};
        ans[0][0]=1;


    	for(int i=0;i<grid.size();i++)
    	{
    		for(int j=0;j<grid[0].size();j++)
    		{

    			if(grid[i][j]==1)
    				ans[i][j]=0;
    			else
    			{
    				if(i>=1)
    					ans[i][j]+=ans[i-1][j];
    				if(j>=1)
    					ans[i][j]+=ans[i][j-1];
    			}
    		}
    	}


    	return ans[grid.size()-1][grid[0].size()-1];
    }
};