LeetCode刷题：741. Cherry Pickup —摘樱桃 动态规划
原题链接：https://leetcode.com/problems/cherry-pickup/
In a 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;
- -1 means the cell contains a thorn that blocks your way.
Your task is to collect maximum number of cherries possible by following the rules below:
- Starting at the position (0, 0) and reaching (N-1, N-1) by moving right or down through valid path cells (cells with value 0 or 1);
- After reaching (N-1, N-1), returning to (0, 0) by moving left or up through valid path cells;
- When passing through a path cell containing a cherry, you pick it up and the cell becomes an empty cell (0);
- If there i