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
17 # merge sort each two linked list
18 l1 = self.mergeKLists(lists[:len(lists)/2])
19 l2 = self.mergeKLists(lists)
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
思路：
总体的思路是模仿归并排序。
这里给的参数是多个链表的头结点数组，将头节点数组不断二分；直到只剩下一个头结点，返回该头节点到上一层，并在上一层中将两个有序链表合并。
将两个有序链表merge的代码和思路，在这篇日志中可以看到
http://www.cnblogs.com/xbf9xbf/p/4186905.html
另，网上还有一种用堆的方法，后续再去试探这种方法，并把另一种方法的代码补上。
另，关于该问题的算法复杂度O(nklogk) （n为单个链表的最大长度，k为链表个数），个人觉得下面这篇日志表述的比较好，共享一下
http://www.tuicool.com/articles/ZnuEVfJ
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