leetcode 【 Merge k Sorted Lists 】python 实现

题目：

Merge k sorted linked lists and return it as one sorted list. Analyze and describe its complexity.

代码：oj测试通过 Runtime: 231 ms

 1 # Definition for singly-linked list.
 2 # class ListNode:
 3 #     def __init__(self, x):
 4 #         self.val = x
 5 #         self.next = None
 6 
 7 class Solution:
 8     # @param a list of ListNode
 9     # @return a ListNode
10     def mergeKLists(self, lists):
11         # none
12         if len(lists) == 0:
13             return None
14         # only one list
15         if len(lists) == 1:
16             return lists[0]
17         # merge sort each two linked list
18         l1 = self.mergeKLists(lists[:len(lists)/2])
19         l2 = self.mergeKLists(lists[len(lists)/2:])
20         head = self.mergeTwoLists(l1,l2)
21         return head
22             
23     # merge two sorted linked list    
24     def mergeTwoLists(self, l1, l2):
25         if l1 is None:
26             return l2
27         if l2 is None:
28             return l1
29         p = ListNode(0)
30         dummyhead = p
31         while l1 is not None and l2 is not None:
32             if l1.val < l2.val:
33                 p.next = l1
34                 l1 = l1.next
35                 p = p.next
36             else:
37                 p.next = l2
38                 l2 = l2.next
39                 p = p.next
40         if l1 is None:
41             p.next = l2
42         else:
43             p.next = l1
44         return dummyhead.next