Common patterns for solving Linked List problems.

1. The Dummy Node Trick

The "dummy node" is a placeholder node used to simplify edge cases in linked list operations. Whether you're reversing a sublist, merging two lists, or removing elements, a dummy node acts as a stable anchor. By attaching the actual list to the dummy node, you can avoid tedious checks for operations involving the head.

Why it’s useful:

• Reduces the need for special handling of the head node.
• Streamlines code for insertion and deletion.

Example Use Case: Merging two sorted linked lists.

2. Slow and Fast Pointer Technique

Also called the "Tortoise and Hare" method, this pattern involves using two pointers moving at different speeds. It’s a powerful tool for problems involving cycles, middle elements, or determining the length of a list.

Common Applications:

• Detecting cycles in a linked list.
• Finding the middle node in a single traversal.
• Determining if a list has an odd or even length.

Example Use Case: Detecting a loop in a linked list.

3. Reversal Techniques

Reversing a linked list is a foundational operation. Whether it’s the entire list or just a segment, understanding reversal is key for many advanced problems.

Approaches:

• Iterative: Modify next pointers as you traverse the list.
• Recursive: Reverse the rest of the list, then adjust pointers during unwinding.

Example Use Case: Reversing a sublist within a linked list.

4. The Two-Pass Method

Sometimes, solving a problem in a single pass is challenging or requires complex logic. The two-pass method processes the list twice, simplifying the algorithm at the expense of an extra traversal.

Example Use Case: Removing the nth node from the end of the list.

5. Sentinel Nodes

Similar to the dummy node but used specifically to simplify boundary conditions. Sentinel nodes can mark the beginning or end of the list.

Example Use Case: Maintaining a circular linked list.