题解 | #链表中的节点每k个一组翻转#

O(n), O(n/k）

# class ListNode:
#     def __init__(self, x):
#         self.val = x
#         self.next = None

#
# 
# @param head ListNode类 
# @param k int整型 
# @return ListNode类
#
class Solution:
    def reverseKGroup(self , head , k ):
        # write code here
        def reverse(a, b):           
            cur, nxt = a, a
            pre = None
            while cur!=b:
                nxt = cur.next
                cur.next = pre
                pre = cur
                cur = nxt
            return pre
        if not head:
            return
        a,b = head, head
        for i in range(k):
            if not b:
                return head
            b = b.next
        newHead = reverse(a, b)
        a.next = self.reverseKGroup(b, k)
        return newHead