1 题目
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。
2 解析
（1）方法一：递归
（2）方法二：迭代
3 Python实现
class Solution:
# 方法一
'''
def mergeTwoLists(self, l1: ListNode, l2: ListNode) -> ListNode:
if l1 is None:
return l2
elif l2 is None:
return l1
elif l1.val< l2.val:
l1.next = self.mergeTwoLists(l1.next,l2)
return l1
else :
l2.next = self.mergeTwoLists(l1, l2.next)
return l2
'''
# 方法二：迭代法
def mergeTwoLists(self, l1: ListNode, l2: ListNode) -> ListNode:
head = ListNode(-1)
prev = head
while l1 and l2 :
if l1.val <=l2.val:
prev.next = l1
l1 = l1.next
else:
prev.next = l2
l2 = l2.next
prev = prev.next
prev.next = l1 if l1 is not None else l2
return head.next
