21. Merge Two Sorted Lists
- 描述：
将两个有序链表进行合并，合并之后的链表也是有序链表
- 思路：
递归 - 代码
Definition for singly-linked list.
class ListNode:
def init(self, x):
self.val = x
self.next = None
class Solution:
def mergeTwoLists(self, l1, l2):
# if not l1 or not l2:
# return l1 or l2
if l1==None:
return l2
if l2==None:
return l1
if l1.val < l2.val:
l1.next = self.mergeTwoLists(l1.next, l2)
return l1
else:
l2.next = self.mergeTwoLists(l1, l2.next)
return l2
