礼物的最大价值

class Solution {
public:
    int getMaxValue(vector<vector<int>>& grid) {
        int n=grid.size(),m=grid[0].size();
        vector<vector<int>> f(n,vector<int> (m,0));//f[i][j]表示走到ij可以拿到的最大价值
        for (int i = 0; i < n; i ++ )
            for (int j = 0; j < m; j ++ )
            {
                f[i][j]=grid[i][j];
                if(i)   f[i][j]+=f[i-1][j];
                if(j)   f[i][j]=max(f[i][j],f[i][j-1]+grid[i][j]);
            }
        return f[n-1][m-1];
    }
};