class Solution {
    public int minPathSum(int[][] grid) {
        if(grid == null || grid.length == 0 || grid[0].length == 0)
            return 0;
        int n = grid.length, m = grid[0].length;
        int[][] f = new int[n][m];
        f[0][0] = grid[0][0];
        for(int i = 1; i < n; i ++ )
            f[i][0] = f[i - 1][0] + grid[i][0];
        for(int i = 1; i < m; i ++ )
            f[0][i] = f[0][i - 1] + grid[0][i];

        for(int i = 1; i < n; i ++ )
            for(int j = 1; j < m; j ++ )
                f[i][j] = Math.min(f[i - 1][j], f[i][j - 1]) + grid[i][j];

        return f[n - 1][m - 1];
    }
}