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给你一个 n x n 的网格 grid ，代表一块樱桃地，每个格子由以下三种数字的一种来表示：
0 表示这个格子是空的，所以你可以穿过它。1 表示这个格子里装着一个樱桃，你可以摘到樱桃然后穿过它。-1 表示这个格子里有荆棘，挡着你的路。请你统计并返回：在遵守下列规则的情况下，能摘到的最多樱桃数：
\n\n(0, 0) 出发，最后到达 (n - 1, n - 1) ，只能向下或向右走，并且只能穿越有效的格子（即只可以穿过值为 0 或者 1 的格子）；(n - 1, n - 1) 后，你要继续走，直到返回到 (0, 0) ，只能向上或向左走，并且只能穿越有效的格子；0 ）；(0, 0) 和 (n - 1, n - 1) 之间不存在一条可经过的路径，则无法摘到任何一个樱桃。\n\n
示例 1：
\n\n\n输入：grid = [[0,1,-1],[1,0,-1],[1,1,1]]\n输出：5\n解释：玩家从 (0, 0) 出发：向下、向下、向右、向右移动至 (2, 2) 。\n在这一次行程中捡到 4 个樱桃，矩阵变成 [[0,1,-1],[0,0,-1],[0,0,0]] 。\n然后，玩家向左、向上、向上、向左返回起点，再捡到 1 个樱桃。\n总共捡到 5 个樱桃，这是最大可能值。\n\n\n
示例 2：
\n\n\n输入：grid = [[1,1,-1],[1,-1,1],[-1,1,1]]\n输出：0\n\n\n
\n\n
提示：
\n\nn == grid.lengthn == grid[i].length1 <= n <= 50grid[i][j] 为 -1、0 或 1grid[0][0] != -1grid[n - 1][n - 1] != -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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\\u6a21\\u5757\\u4e2d\\u63d0\\u4f9b\\uff1ahttps:\\/\\/www.rubydoc.info\\/github\\/kanwei\\/algorithms\\/Algorithms<\\/p>\"],\"swift\":[\"Swift\",\" \\u7248\\u672c\\uff1a \\u6211\\u4eec\\u901a\\u5e38\\u4fdd\\u8bc1\\u66f4\\u65b0\\u5230 Apple\\u653e\\u51fa\\u7684\\u6700\\u65b0\\u7248Swift<\\/a>\\u3002\\u5982\\u679c\\u60a8\\u53d1\\u73b0Swift\\u4e0d\\u662f\\u6700\\u65b0\\u7248\\u7684\\uff0c\\u8bf7\\u8054\\u7cfb\\u6211\\u4eec\\uff01\\u6211\\u4eec\\u5c06\\u5c3d\\u5feb\\u66f4\\u65b0\\u3002<\\/p>\"],\"golang\":[\"Go\",\" \\u7248\\u672c\\uff1a \\u652f\\u6301 https:\\/\\/godoc.org\\/github.com\\/emirpasic\\/gods@v1.18.1<\\/a> \\u7b2c\\u4e09\\u65b9\\u5e93\\u3002<\\/p>\"],\"python3\":[\"Python3\",\" \\u7248\\u672c\\uff1a \\u4e3a\\u4e86\\u65b9\\u4fbf\\u8d77\\u89c1\\uff0c\\u5927\\u90e8\\u5206\\u5e38\\u7528\\u5e93\\u5df2\\u7ecf\\u88ab\\u81ea\\u52a8 \\u5bfc\\u5165\\uff0c\\u5982array<\\/a>, bisect<\\/a>, collections<\\/a>\\u3002 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