Linked list edge cases I kept getting wrong

A checklist I now run through for every linked list method: - Empty list: does head (and tail) stay null correctly? - One element: removing it must clear both head AND tail. - Adding to the front of an empty list: tail needs to be set too. - Removing the last node in a singly linked list: you need the node BEFORE it, so you walk the list. - Size: update it in every path, including early returns. - Doubly linked: every change touches two pointers. Draw the arrows before writing code. Nearly all of my failed tests traced back to one of these.