将两个升序链表合并为一个新的 升序 链表并返回。新链表是通过拼接给定的两个链表的所有节点组成的。

输入：l1 = [1,2,4], l2 = [1,3,4]
输出：[1,1,2,3,4,4]

示例 2：

输入：l1 = [], l2 = []
输出：[]

示例 3：

输入：l1 = [], l2 = [0]
输出：[0]

简单粗暴方式，不足为没有利用空间

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, val=0, next=None):
#         self.val = val
#         self.next = next
class Solution:
    def mergeTwoLists(self, l1: ListNode, l2: ListNode) -> ListNode:
        l = ListNode()
        p = l
        while(l1 and l2):
            if(l1.val<l2.val):
                temp = ListNode(l1.val)
                l1 = l1.next      
            else:
                temp = ListNode(l2.val)
                l2 = l2.next
            l.next = temp
            l = l.next
        
        l.next = l1 if(l1) else l2
        return p.next