You are given an n x n grid representing a field of cherries, each cell is one of three possible integers.
0 means the cell is empty, so you can pass through,1 means the cell contains a cherry that you can pick up and pass through, or-1 means the cell contains a thorn that blocks your way.Return the maximum number of cherries you can collect by following the rules below:
\n\n(0, 0) and reaching (n - 1, n - 1) by moving right or down through valid path cells (cells with value 0 or 1).(n - 1, n - 1), returning to (0, 0) by moving left or up through valid path cells.0.(0, 0) and (n - 1, n - 1), then no cherries can be collected.\n
Example 1:
\n![\"\"](\"https://assets.leetcode.com/uploads/2020/12/14/grid.jpg\")
\n\nInput: grid = [[0,1,-1],[1,0,-1],[1,1,1]]\nOutput: 5\nExplanation: The player started at (0, 0) and went down, down, right right to reach (2, 2).\n4 cherries were picked up during this single trip, and the matrix becomes [[0,1,-1],[0,0,-1],[0,0,0]].\nThen, the player went left, up, up, left to return home, picking up one more cherry.\nThe total number of cherries picked up is 5, and this is the maximum possible.\n\n\n
Example 2:
\n\n\nInput: grid = [[1,1,-1],[1,-1,1],[-1,1,1]]\nOutput: 0\n\n\n
\n
Constraints:
\n\nn == grid.lengthn == grid[i].length1 <= n <= 50grid[i][j] is -1, 0, or 1.grid[0][0] != -1grid[n - 1][n - 1] != -1一个N x N的网格(grid) 代表了一块樱桃地，每个格子由以下三种数字的一种来表示：
你的任务是在遵守下列规则的情况下，尽可能的摘到最多樱桃：
\n\n示例 1:
\n\n\n输入: grid =\n[[0, 1, -1],\n [1, 0, -1],\n [1, 1, 1]]\n输出: 5\n解释： \n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)。\n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]]。\n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。\n在旅程中，总共摘到了5颗樱桃，这是可以摘到的最大值了。\n\n\n
说明:
\n\ngrid 是一个 N * N 的二维数组，N的取值范围是1 <= N <= 50。grid[i][j] 都是集合 {-1, 0, 1}其中的一个数。grid[0][0] 和终点 grid[N-1][N-1] 的值都不会是 -1。\\u7248\\u672c\\uff1a \\u7f16\\u8bd1\\u65f6\\uff0c\\u5c06\\u4f1a\\u91c7\\u7528 \\u4e3a\\u4e86\\u4f7f\\u7528\\u65b9\\u4fbf\\uff0c\\u5927\\u90e8\\u5206\\u6807\\u51c6\\u5e93\\u7684\\u5934\\u6587\\u4ef6\\u5df2\\u7ecf\\u88ab\\u81ea\\u52a8\\u5bfc\\u5165\\u3002<\\/p>\"],\"java\":[\"Java\",\" \\u7248\\u672c\\uff1a \\u4e3a\\u4e86\\u65b9\\u4fbf\\u8d77\\u89c1\\uff0c\\u5927\\u90e8\\u5206\\u6807\\u51c6\\u5e93\\u7684\\u5934\\u6587\\u4ef6\\u5df2\\u88ab\\u5bfc\\u5165\\u3002<\\/p>\\r\\n\\r\\n \\u5305\\u542b Pair \\u7c7b: https:\\/\\/docs.oracle.com\\/javase\\/8\\/javafx\\/api\\/javafx\\/util\\/Pair.html <\\/p>\"],\"python\":[\"Python\",\" \\u7248\\u672c\\uff1a \\u4e3a\\u4e86\\u65b9\\u4fbf\\u8d77\\u89c1\\uff0c\\u5927\\u90e8\\u5206\\u5e38\\u7528\\u5e93\\u5df2\\u7ecf\\u88ab\\u81ea\\u52a8 \\u5bfc\\u5165\\uff0c\\u5982\\uff1aarray<\\/a>, bisect<\\/a>, 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