【LEETCODE】148- Sort List [Python]

Sort a linked list in O(n log n) time using constant space complexity.

题意：

对一个链表排序，O(n log n) time ， constant space complexity

思路：

根据题意对时间和空间复杂度的要求，此处排序用归并

参考：

归并排序：

http://blog.csdn.net/littlethunder/article/details/9472301

http://bookshadow.com/weblog/2014/11/21/leetcode-sort-list/

Python

# Definition for singly-linked list.# class ListNode(object):#     def __init__(self, x):#         self.val = x#         self.next = Noneclass Solution(object):    def sortList(self, head):        """        :type head: ListNode        :rtype: ListNode        """                if head is None or head.next is None:            return head                mid=self.getmiddle(head)        lHead=head        rHead=mid.next        mid.next=None                return self.merge(self.sortList(lHead),self.sortList(rHead))        def getmiddle(self,head):                if head is None:            return head                    fast=slow=head                while fast.next and fast.next.next:            slow=slow.next            fast=fast.next.next                return slow                def merge(self,lHead,rHead):        dumNode=ListNode(0)        dumHead=dumNode                i=lHead        j=rHead                while i and j:            if i.val<j.val:                dumNode.next=i                i=i.next            else:                dumNode.next=j                j=j.next            dumNode=dumNode.next                if i:            dumNode.next=i        if j:            dumNode.next=j                return dumHead.next