@@ -282,7 +282,6 @@ class Solution:
282282```
283283- 7 or 9 等于 7
284284- None and 7 等于 None
285- - sorted用在这里为了保证 l1 的值小于等于 l2 的值
286285## [ 23. Merge k Sorted Lists 4行] ( https://leetcode.com/problems/merge-k-sorted-lists/ )
287286``` python
288287# Definition for singly-linked list.
@@ -5523,6 +5522,23 @@ class Solution:
55235522- 空间复杂度:O(logN)
55245523- x^4 = x^2 ** x^2, x^5 = x^2 * x^2 * x, 借此方法可以缩减计算量
55255524
5525+ ☄ ** 总结**
5526+ #### [ 21. 合并两个有序链表] ( https://leetcode-cn.com/problems/merge-two-sorted-lists/ )
5527+ ``` python
5528+ # Definition for singly-linked list.
5529+ # class ListNode:
5530+ # def __init__(self, x):
5531+ # self.val = x
5532+ # self.next = None
5533+ 5534+ class Solution :
5535+ def mergeTwoLists (self l1 : ListNode, l2 : ListNode) -> ListNode:
5536+ if l1 and l2:
5537+ if l1.val > l2.val: l1, l2 = l2, l1
5538+ l1.next = self .mergeTwoLists(l1.next, l2)
5539+ return l1 or l2
5540+ ```
5541+ 55265542# 常用技巧总结
55275543- set 中的 in 操作时间复杂度为 O(1)
55285544- dict.get 可以设置预设值,避免取到不存在的 key 时报错
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