Given a singly linked list, group all odd nodes together followed by the even nodes. Please note here we are talking about the node number and not the value in the nodes.

You should try to do it in place. The program should run in O(1) space complexity and O(nodes) time complexity.
Example: ?Given1->2->3->4->5->NULL, ? ?return1->3->5->2->4->NULL.

想的是一個一個調換， 結果發現需要用到的變量太多了，?

把奇偶結點分為兩個鏈表最后合在一起比較簡單。