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Computer Science Introduction to Data Structures Merge Sort and Linked Lists The Divide Step

Would we ever actually call split on a linked list with one node? I would think that would result in merge sort.

returning that item as naively sorted before it could be split. Thus you would never have a LinkedList with a value of None? Likewise, if the head was None then it would never be evaluated in the split function either since Merge_Sort would return it?

1 Answer

Chris Freeman
Chris Freeman
Treehouse Moderator 68,082 Points

Your observation is correct. As implemented, the main merge_sort code would quickly return if the linked_list contained one or fewer elements. Then why might the split function need to also content with a single node or empty list?

It is a good programming practice also to cover boundary conditions within the split function so it may be reused by other functions that need to split a linked list. This also lets the split function focus on its core job of always returning two object regardless of the input given.

A follow up question one might ask: if split handles the trivial list, why does merge_sort need to check for trivial cases? merge_sort needs to return on the trivial cases to end the recursive descent. Otherwise, split would continue to return the linked_list as left_half and none.

Post back if you need more help. Good luck!!!