3)The Complete Linked List Roadmap: 10 Algorithms from Beginner to Expert (2026 Guide)

“Arrays are for storing data. Linked Lists are for manipulating references.” Arrays are static; Linked Lists are dynamic. If you want to work on Blockchains or Low-Level Memory Management (like inside the Linux Kernel), you must master pointer surgery.

This guide covers the 10 Essential Linked List Patterns that separate “Code Monkeys” from “Software Engineers.”

Linked Lists are the “Boogeyman” of coding interviews. Why? Because unlike arrays, you don’t have indices ($arr[i]$). You only have pointers ($\to$). One wrong move, one broken link, and you lose the entire list (or crash the program).

But here is the secret: Linked List problems are rarely about algorithms. They are about “Pointer Surgery.”

Once you learn the Dummy Node trick and the Fast & Slow Pointer technique, 90% of problems become trivial. Here is the complete roadmap.

Table of Contents

Part 1: The “Tortoise & Hare” (Cycle Patterns)

The most famous pattern in computer science. How to traverse without knowing the length.

1. Detect Cycle (Floyd’s Cycle Finding)

The Scenario: Does the list loop back on itself?
The Logic: Use two pointers.
- Slow: Moves 1 step.
- Fast: Moves 2 steps.
- If Fast laps Slow (they meet), there is a cycle.
- If Fast reaches NULL, there is no cycle.

2. Find the Start of the Cycle

The Scenario: “I know there is a loop. Where does it begin?”
The Logic: (Math Heavy).
- Once Slow and Fast meet, keep Slow there.
- Move Fast back to Head.
- Move both 1 step at a time.
- The point where they meet again is the Start Node.

3. Middle of Linked List

The Scenario: Find the center node in one pass.
The Logic: When Fast (2x speed) reaches the end, Slow (1x speed) is exactly at the middle.

Part 2: The “Rewiring” Pattern (Reversal)

Changing the direction of arrows without losing data.

4. Reverse a Linked List (Iterative & Recursive)

The Scenario: Turn 1 -> 2 -> 3 into 3 -> 2 -> 1.
The “Professor’s Rule”: You need 3 Pointers.
- Prev (holds the new tail).
- Curr (the node we are working on).
- Next (saves the future path so we don’t lose it).
- Logic: curr->next = prev; prev = curr; curr = next;

5. Palindrome Linked List

The Scenario: Is 1 -> 2 -> 2 -> 1 a palindrome?
The Logic: You cannot go backward in a Singly Linked List.
1. Find the Middle (using Slow/Fast).
2. Reverse the second half of the list.
3. Compare the First Half vs. the Reversed Second Half.

Part 3: The “Dummy Node” Pattern (Edge Cases)

The #1 Trick to write clean code.

6. Remove N-th Node From End

The Scenario: Delete the 2nd node from the last.
The Problem: What if you need to delete the Head?
The Solution: Create a Dummy Node pointing to Head.
- Move Fast pointer N steps ahead.
- Move Slow and Fast together until Fast hits the end.
- Slow is now right before the target. Delete it.

7. Merge Two Sorted Lists

The Scenario: Zip two sorted lists together.
The Logic: Use a Dummy Node as the “Anchor.”
- Compare L1.val and L2.val.
- Attach the smaller one to Current.next.
- Move pointers forward.

Part 4: The “Advanced” Pattern (Deep Manipulation)

These are “Hard” on LeetCode. They test memory management.

8. Intersection of Two Linked Lists

The Scenario: Where do two Y-shaped lists merge?
The Logic:
- Pointer A walks List A, then jumps to List B.
- Pointer B walks List B, then jumps to List A.
- They will meet at the intersection point because they walk the same total distance ($LenA + LenB$).

9. Copy List with Random Pointer

The Scenario: Duplicate a list where nodes have a Next pointer AND a Random pointer.
The Logic: Use a Hash Map OR the Interleaving Method (O(1) Space).
- Interleaving: Insert copy of Node A right after Node A (A -> A' -> B -> B').
- Connect random pointers.
- Separate the lists.

10. Reverse Nodes in K-Group

The Scenario: Reverse every K nodes (e.g., 1-2, 3-4).
The Logic: This is the “Final Boss.”
- Check if there are K nodes left.
- If yes, use the standard Reverse logic for those K nodes.
- Connect the Prev group tail to the new Head.
- Recursively or Iteratively continue.

The Professor’s Cheat Code Sheet

Stick this table at the bottom of your post. It simplifies the chaos.

Problem Goal	The Strategy	Complexity
Cycle Detection	Floyd’s (Slow/Fast)	O(N) Time, O(1) Space
Find Middle	Slow/Fast Pointers	O(N) Time, O(1) Space
Reverse List	3-Pointer (Prev, Curr, Next)	O(N) Time, O(1) Space
Delete Head/Node	Dummy Node	Handles Edge Cases
N-th from End	Two Pointer Gap	Single Pass
Intersection	Switch Heads (A->B, B->A)	O(N+M) Time
Deep Copy (Random)	Interleaving / Hash Map	O(N) Time
Palindrome	Find Mid + Reverse Half	O(N) Time

Professor’s Advice for Teaching This

“Students, listen closely.

Always draw boxes and arrows. If you try to do Linked Lists in your head, you will fail.

The Dummy Node is your best friend. It saves you from writing if (head == null) ten times.

Fast & Slow is not just for cycles; it’s for finding the Middle and Palindromes too.

Master these three tips, and you master the Linked List.”

The Complete Linked List Roadmap: 10 Algorithms from Beginner to Expert (2026 Guide)

Linked List Algorithms for Interview Floyd’s Cycle Detection Explained Reverse Linked List Iterative vs Recursive Merge Two Sorted Lists Solution

YouTube Channels:
Trendy VS Vlogs
VS Coding Academy

Join Our WhatsApp Channel for the latest job opportunities and updates:
VS_CODING_ACADEMY WhatsApp Channel

Join Our Telegram Channel for the latest job opportunities and updates: https://t.me/vscodingacademy

Open our site in Telegram Bot: https://t.me/vscodingacademy_bot

For DSA Guide: https://vscodingacademy.com/category/dsa-guide/