What are the core concepts covered in Linked Lists & Floyd's Cycle Detection (Tortoise & Hare)?

Node pointer chaining (val, next); In-place iterative reversal of a linked list in O(n) time and O(1) space; Floyd's Tortoise and Hare two-pointer cycle detection algorithm

Intermediate 18 min readModule: Module 3: Singly & Doubly Linked Lists

Linked Lists & Floyd's Cycle Detection (Tortoise & Hare)

Implement linked list nodes, reverse lists in-place in O(n) time, and detect circular loops.

What You Will Learn in This Lesson

Node pointer chaining (val, next)
In-place iterative reversal of a linked list in O(n) time and O(1) space
Floyd's Tortoise and Hare two-pointer cycle detection algorithm

Introduction & Core Concept

A Linked List is a linear data structure where elements are not stored at contiguous memory locations. Instead, each node contains data and a pointer to the next node.

WHY DOES THIS MATTER IN THE REAL WORLD?

Linked lists allow O(1) constant-time insertions at the head without shifting array memory.

Linked List In-Place Reversal

javascript

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
class ListNode {
  constructor(val, next = null) { this.val = val; this.next = next; }
}
 
function reverseList(head) {
  let prev = null, current = head;
  while (current) {
    const nextTemp = current.next;
    current.next = prev;
    prev = current;
    current = nextTemp;
  }
  return prev;
}
 
const list = new ListNode(1, new ListNode(2, new ListNode(3)));
console.log("Reversed Head Val:", reverseList(list).val);

Line-by-Line Technical Breakdown

1Fast pointer moves 2 steps while slow moves 1 step; if they meet, a cycle exists.

Try It Yourself (Interactive Editor)

Modify the code in real-time and click Run to test live browser output and console logs.

Intelligent Code Runner & Live Sandbox[JAVASCRIPT]

JAVASCRIPT SOURCE EDITOR

Interactive Live Code

>Reversed Head Val: 3

Industry Best Practices & Professional Standards

Always use dummy head pointers to simplify edge cases in linked list mutations.

Lesson Summary & Core Takeaways

Linked lists provide flexible pointer-based dynamic node structures.