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

题目来源：

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

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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。

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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。

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代码（python）：

 # Definition for singly-linked list.
 # class ListNode(object):
 #     def __init__(self, x):
 #         self.val = x
 #         self.next = None
 class Solution(object):
     def reverse(self,start,end):
         nhead = ListNode(0)
         nhead.next = start
         while nhead.next != end:
             tmp = start.next
             start.next = tmp.next
             tmp.next = nhead.next
             nhead.next = tmp
         return [end,start]
     def reverseKGroup(self, head, k):
         """
         :type head: ListNode
         :type k: int
         :rtype: ListNode
         """
         ans = ListNode(0)
         if head == None:
             return None
         ans.next = head
         start = ans
         while start.next != None:
             end = start
             i = 0
             while i < k - 1:
                 end = end.next
                 if end.next == None:
                     return ans.next
                 i += 1
             tmp = self.reverse(start.next,end.next)
             start.next = tmp[0]
             start = tmp[1]
         return ans.next

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