合并两个链表

一、合并两个链表

1.1、定义链表节点

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, x):
#         self.val = x
#         self.next = None

1.2、使用递归

class Solution:
    def mergeTwoLists(self, l1: ListNode, l2: ListNode) -> ListNode:
        if l1 is None:
            return l2
        if l2 is None:
            return l1
        # 第一步: 那个列表的头部元素小，将其作为新列表的头部
        if l1.val  ListNode:
        
        pahead = ListNode(-1)
        prev = pahead
        while l1 and l2:
            if l1.val