Re-ordering a Linked List in Python

Question

I realize this sort of data structure is better done with built in list type, but I\'m trying to understand this more for academic reasons. Given that I have a linked list like

Answer 1

Sometimes the best thing is to first think "how fast would an optimal solution be?" This seems pretty apparently O(length), so something that runs through the list, preferably once, is going to be about as good as you can do.

Given that, you're probably going to find the simplest choice is best. In pseudocode, it would be

 get the first element in left
 get the second element in right
 append them to a new list as right->left
 repeat until you run out of list.

As Matt and Jodaka note, you do need to decide what to do with an odd-length list, if an odd-length list is permitted at all.