剑指 Offer 25. 合并两个排序的链表

输入两个递增排序的链表，合并这两个链表并使新链表中的节点仍然是递增排序的。

示例1：

输入：1->2->4, 1->3->4
输出：1->1->2->3->4->4

限制：

• 0 <= 链表长度 <= 1000

Python 解答：

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

class Solution:
    def mergeTwoLists(self, l1: ListNode, l2: ListNode) -> ListNode:
        head = ListNode(0)
        p = head
        while l1 and l2:
            if l1.val < l2.val:
                p.next = l1
                l1 = l1.next
                p = p.next
            else:
                p.next = l2
                l2 = l2.next
                p = p.next
        if l1:
            p.next = l1
        if l2:
            p.next = l2
        return head.next