Unique Paths 入门级动态规划，我一开始用递归做了一下，直接超时了//// 2333

虽然是 hard 类的题目，但其实也很简单。不过代码如果想要既美观又高效，可能就要费点功夫了。题目链接: Jump Game, Jump Game II。

题目链接: https://leetcode.com/problems/linked-list-cycle-ii/description/

题目链接: https://leetcode.com/problems/reverse-linked-list-ii/description/

题目链接: https://leetcode.com/problems/swap-nodes-in-pairs/description/

链表套餐: https://leetcode.com/tag/linked-list/

Given n pairs of parentheses, write a function to generate all combinations of well-formed parentheses.

Given a linked list, remove the $n_{th}$ node from the end of list and return its head.

题目大意：对于一个给出的数字串，输出其可能的在手机键盘上代表的字符串，如对于数字串“23”。

其可能代表的字符串便有”ad”, “ae”, “af”, “bd”, “be”, “bf”, “cd”, “ce”, “cf”

给于一个整型数字范围在1-3999，将它转化为罗马数字

leetcode 11.盛最多水的容器