DP problems on the grid

1463. Cherry Pickup II

C++ code[1]

class Solution {
public:
    int cherryPickup(vector<vector<int>>& grid) {
        int R= grid.size(), C = grid[0].size();
        vector<vector<int>> dp(C, vector<int>(C, INT_MIN));
        dp[0][C-1] = grid[0][0] + grid[0][C-1];
        for (int r =1;r<R;++r)
        {
            vector<vector<int>> dp_new(C, vector<int>(C, INT_MIN));
            for (int i=0;i<C;++i)
                for (int j=0; j<C;++j)
                {
                    for(int a = i-1; a<=i+1;++a)
                        for(int b = j-1;b<=j+1;++b)
                        {
                            if(a<0 or a>=C or b<0 or b>=C)continue;
                            dp_new[i][j] =  max(dp_new[i][j], dp[a][b]+grid[r][i]+(i==j?0:grid[r][j]));   
                        }
                }
            dp = dp_new;
        }
        int ret = INT_MIN;
        for(int i=0;i<C;++i)
            for(int j=0;j<C;++j)
                ret = max(ret, dp[i][j]);
        return ret;
    }
};

Reference

[1]https://youtu.be/2iuqobSv9NU