Merge Two Sorted Lists,自己的代码一遍通过

题目描述：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.其实题目理解起来很简单，就是讲两个有序的链表合并成一个新的链表。

 1 def mergeTwoLists(self, l1, l2):
 2         if l1 == None:
 3             return l2
 4         elif l2 == None:
 5             return l1
 6         elif l1 == None and l2 == None:
 7             return None
 8         else:
 9             p1 = l1
10             p2 = l2
11             if p1.val > p2.val:
12                 l = p2
13                 p = p2
14                 p2 = p2.next
15                 while p1 and p2:
16                     if p1.val > p2.val:
17                         p.next = p2
18                         p = p2
19                         p2 = p2.next
20
21                     else:
22                         p.next = p1
23                         p = p1
24                         p1 = p1.next
25
26                 if p1:
27                     while p1:
28                         p.next = p1
29                         p = p1
30                         p1 = p1.next
31                     return l
32                 if p2:
33                     while p2:
34                         p.next = p2
35                         p = p2
36                         p2 = p2.next
37                     return l
38             else:
39                 l = p1
40                 p = p1
41                 p1 = p1.next
42                 while p1 and p2:
43                     if p1.val > p2.val:
44                         p.next = p2
45                         p = p2
46                         p2 = p2.next
47
48                     else:
49                         p.next = p1
50                         p = p1
51                         p1 = p1.next
52
53                 if p1:
54                     while p1:
55                         p.next = p1
56                         p = p1
57                         p1 = p1.next
58                     return l
59                 if p2:
60                     while p2:
61                         p.next = p2
62                         p = p2
63                         p2 = p2.next
64                     return l