[Leetcode] Unique Paths II

// Recursion 大数据集无法通过
class Solution {
private:
    int _count;
    
public:
    int uniquePathsWithObstacles(vector<vector<int> > &grid) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        _count = 0;
        dfs(grid, 0, 0);
        return _count;
    }
    
    void dfs(vector<vector<int> > &grid, int i, int j)
    {        
        int r = grid.size();
        int c = grid[0].size();
        
        if (i == r || i < 0 || j == c || j < 0)
            return;
                    
        if (grid[i][j] == 1)
            return;
        else
        {
            if (i == r - 1 && j == c - 1)
            {
                ++_count;
                return;
            }
            else
            {
                dfs(grid, i + 1, j);
                dfs(grid, i, j + 1);
            }
        }
    }
};

// DP
class Solution {
public:
    int uniquePathsWithObstacles(vector<vector<int> > &grid) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        if (grid.size() == 0) return 0;
        
        int r = grid.size();
        int c = grid[0].size();
        if (grid[r - 1][c - 1] == 1 || grid[0][0] == 1)
            return 0;
        
        int mat[105][105];
        
        mat[r - 1][c - 1] = 1;
        for (int i = c - 2; i >= 0; --i)        
        {
            if (grid[r - 1][i] == 1)
                mat[r - 1][i] = 0;
            else
                mat[r - 1][i] = mat[r - 1][i + 1];
        }            
        
        for (int i = r - 2; i >= 0; --i)
        {
            if (grid[i][c - 1] == 1)
                mat[i][c - 1] = 0;
            else
                mat[i][c - 1] = mat[i + 1][c - 1];
        }
            

        for (int i = r - 2; i >= 0; --i)
        {
            for (int j = c - 2; j >= 0; --j)
            {
                if (grid[i][j] == 0)
                    mat[i][j] = mat[i + 1][j] + mat[i][j + 1];
                else
                    mat[i][j] = 0;
            }
        }
        
        return mat[0][0];
    }
};