741. cherry picking

An N x N grid (grid) represents a cherry, each grid is represented by one of three numbers:

• 0 indicates that the grid is empty, so you can pass through it.
• 1 indicates that the grid filled with a cherry, then you can pick the cherries through it.
• -1 indicates that the grid has thorns, blocking your way.

Your task is in compliance with the following rules, as far as possible to pick the most cherries:

• Starting from the position (0, 0), and finally to (N-1, N-1), can only go down or right and can only be effective through the lattice (i.e., the lattice can only pass through the value 0 or 1, );
• When reaching the (N-1, N-1) after you go to continue, until it returns to the (0, 0), can go up or to the left, and only through the effective lattice;
• When you pass through the grid comprises a grid and a cherry, you pick the cherries and this grid becomes empty (the value becomes 0);
• If (0, 0), and (N-1, N-1) may be a path does not exist between passes, then there is no pick to be a cherry.

Example 1:

输入: grid =
[[0, 1, -1],
 [1, 0, -1],
 [1, 1,  1]]
输出: 5
解释： 
玩家从（0,0）点出发，经过了向下走，向下走，向右走，向右走，到达了点(2, 2)。
在这趟单程中，总共摘到了4颗樱桃，矩阵变成了[[0,1,-1],[0,0,-1],[0,0,0]]。
接着，这名玩家向左走，向上走，向上走，向左走，返回了起始点，又摘到了1颗樱桃。
在旅程中，总共摘到了5颗樱桃，这是可以摘到的最大值了。

Description:

• gridA  N* Ntwo-dimensional array, N is ranges 1 <= N <= 50.
• Each  grid[i][j]is a collection of  {-1, 0, 1}a number of them.
• We can guarantee the start  grid[0][0] and end  grid[N-1][N-1] values will not be -1.