21. Merge Two Sorted Lists

Merge two sorted linked lists and return it as a new list. The new list should be made by splicing together the nodes of the first two lists.

AC代码：

class Solution(object):
def mergeTwoLists(self, l1, l2):
ret_list = current = ListNode(0)
while l1 is not None and l2 is not None:
if l1.val <= l2.val:
current.next = l1
l1 = l1.next
else:
current.next = l2
l2 = l2.next
current = current.next
if l1 is not None:
current.next = l1
if l2 is not None:
current.next = l2
return ret_list.next

因为都是有序的链表，直接按照大小遍历即可。