合并两个有序链表

好好体会链表的魅力。。。

# 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:
        re=ListNode(0)
        head=re
        while l1 and l2:
            if l1.val<l2.val:
                re.next=ListNode(l1.val)
                l1=l1.next
            else:
                re.next=ListNode(l2.val)
                l2=l2.next
            re=re.next
        if l1:
            re.next=l1
        if l2:
            re.next=l2
        return head.next