Study Plan For Algorithms - Part11

1.合并两个有序链表
题目链接：https://leetcode.cn/problems/merge-two-sorted-lists/
将两个升序链表合并为一个新的 升序 链表并返回。新链表是通过拼接给定的两个链表的所有节点组成的。

class Solution:
    def mergeTwoLists(self, list1: Optional[ListNode], list2: Optional[ListNode]) -> Optional[ListNode]:
        dummy = ListNode()
        curr = dummy

        while list1 and list2:
            if list1.val < list2.val:
                curr.next = list1
                list1 = list1.next
            else:
                curr.next = list2
                list2 = list2.next
            curr = curr.next

        curr.next = list1 if list1 else list2

        return dummy.next

2. 括号生成
题目链接：https://leetcode.cn/problems/generate-parentheses/
数字 n 代表生成括号的对数，请设计一个函数，用于能够生成所有可能的并且 有效的 括号组合。

class Solution:
    def generateParenthesis(self, n: int) -> List[str]:
        result = []
        def backtrack(left, right, current):
            if len(current) == 2 * n:
                result.append(current)
                return
            if left < n:
                backtrack(left + 1, right, current + '(')
            if right < left:
                backtrack(left, right + 1, current + ')')
        backtrack(0, 0, '')
        return result