[LeetCode]题解（python）：025-Reverse Nodes in k-Group

题目来源：

　　https://leetcode.com/problems/reverse-nodes-in-k-group/

题意分析：

　　这道题目和上一题目类似，输入一个链表和一个整型k。每k个翻转一下。不能更改链表的值。

题目思路：

　　这道题目为了更加直观，先写一个翻转链表的函数。接下来就是链表操作。

代码（python）：

 1 # Definition for singly-linked list.
 2 # class ListNode(object):
 3 #     def __init__(self, x):
 4 #         self.val = x
 5 #         self.next = None
 6 class Solution(object):
 7     def reverse(self,start,end):
 8         nhead = ListNode(0)
 9         nhead.next = start
10         while nhead.next != end:
11             tmp = start.next
12             start.next = tmp.next
13             tmp.next = nhead.next
14             nhead.next = tmp
15         return [end,start]
16     def reverseKGroup(self, head, k):
17         """
18         :type head: ListNode
19         :type k: int
20         :rtype: ListNode
21         """
22         ans = ListNode(0)
23         if head == None:
24             return None
25         ans.next = head
26         start = ans
27         while start.next != None:
28             end = start
29             i = 0
30             while i < k - 1:
31                 end = end.next
32                 if end.next == None:
33                     return ans.next
34                 i += 1
35             tmp = self.reverse(start.next,end.next)
36             start.next = tmp[0]
37             start = tmp[1]
38         return ans.next

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