class Solution {
public:
    int minPathSum(vector<vector<int>>& grid) {
        if (grid.empty()) return 0;
        int n = grid.size(), m = grid[0].size();
        vector<vector<int>> f(n, vector<int> (m, INT_MAX));
        for (int i = 0; i < n; i++)
            for (int j = 0; j < m; j++)
                if (!i && !j) f[i][j] = grid[i][j];
                else {
                    if (i) f[i][j] = min(f[i][j], f[i - 1][j] + grid[i][j]);
                    if (j) f[i][j] = min(f[i][j], f[i][j - 1] + grid[i][j]);
                }
        return f[n - 1][m - 1];
    }
};