Reverse Nodes in k-Group (Java)

LeetCode

Given a linked list, reverse the nodes of a linked list k at a time and return its modified list.

If the number of nodes is not a multiple of k then left-out nodes in the end should remain as it is.

You may not alter the values in the nodes, only nodes itself may be changed.

Only constant memory is allowed.

For example,
Given this linked list: 1->2->3->4->5

For k = 2, you should return: 2->1->4->3->5

For k = 3, you should return: 3->2->1->4->5  




solution to solve this question is easy to come out(just reverse list in 

certain range),however, coding this question elegantly is not a easy task. 

I spend much time on writing this question, but the code is not easy for 

reading. After search Internet, I find an very good version below.  

http://www.cnblogs.com/lichen782/p/leetcode_Reverse_Nodes_in_kGroup.html