题目
Merge two sorted linked lists and return it as a sorted list. The list should be made by splicing together the nodes of the first two lists.
解题思路
创建一个dummy的节点，同时遍历两个链表，每次把较小的放到后面，当一个链表结束之后，把另一个链表直接加到后面
代码
class Solution:
def mergeTwoLists(self, l1: ListNode, l2: ListNode) -> ListNode:
dummy = ListNode(0)
pre = dummy
while l1 and l2:
if l1.val < l2.val:
pre.next = l1
l1 = l1.next
else:
pre.next = l2
l2 = l2.next
pre = pre.next
pre.next = l1 if l1 is not None else l2
return dummy.next
