示例 1:
输入: [  [1,3,1],  [1,5,1],  [4,2,1]]输出: 12解释: 路径 1→3→5→2→1 可以拿到最多价值的礼物
来源：力扣（LeetCode）链接：https://leetcode-cn.com/problems/li-wu-de-zui-da-jie-zhi-lcof著作权归领扣网络所有。商业转载请联系官方授权，非商业转载请注明出处。

    public int maxValue(int[][] grid) {        int m = grid.length;         int n = grid[0].length;        for (int i = 0; i < m; i++) {            for (int j = 0; j < n; j++) {                if (i == 0 && j == 0) {                    continue;                }                if (i == 0) {                    grid[i][j] += grid[i][j - 1];                } else if (j == 0) {                    grid[i][j] += grid[i - 1][j];                } else {                    grid[i][j] += Math.max(grid[i][j - 1], grid[i - 1][j]);                }            }        }        int maxValue = grid[m - 1][n - 1];        return maxValue;    }