Circular vs Linear Linked List Key Difference in DSA Typescript - Build Both Approaches

Circular vs Linear Linked List Key Difference

📖 Scenario: Imagine you are managing a playlist of songs. You want to understand how the playlist behaves differently if it loops back to the start after the last song (circular) or stops at the last song (linear).

🎯 Goal: You will create two linked lists: one linear and one circular. Then, you will observe how traversing each list behaves differently.

📋 What You'll Learn

Create a linear linked list with three nodes containing values 10, 20, and 30.

Create a circular linked list with three nodes containing values 10, 20, and 30.

Write a function to traverse and collect values from the linear linked list.

Write a function to traverse and collect values from the circular linked list, stopping after visiting all nodes once.

Print the collected values from both lists to compare their traversal outputs.

💡 Why This Matters

🌍 Real World

Circular linked lists are used in applications like music playlists, where after the last song, the playlist loops back to the first song. Linear linked lists are used in simple queues or stacks where the end is a stopping point.

💼 Career

Understanding the difference between circular and linear linked lists helps in designing efficient data structures for real-time systems, gaming, and resource scheduling in software development.

1

Create a linear linked list with three nodes

Create a class called Node with a constructor that takes value: number and next: Node | null. Then create three nodes with values 10, 20, and 30 linked linearly using next. Assign the first node to a variable called linearHead.

DSA Typescript

// Define Node class and create linear linked list nodes
// Your code here

Hint

Remember, in a linear linked list, the last node's next is null.

2

Create a circular linked list with three nodes

Using the same Node class, create three nodes with values 10, 20, and 30 linked circularly so that the last node's next points back to the first node. Assign the first node to a variable called circularHead.

DSA Typescript

class Node {
    value: number;
    next: Node | null;
    constructor(value: number, next: Node | null = null) {
        this.value = value;
        this.next = next;
    }
}

const node1 = new Node(10);
const node2 = new Node(20);
const node3 = new Node(30);

node1.next = node2;
node2.next = node3;
node3.next = null;

const linearHead = node1;

// Create circular linked list nodes below
// Your code here

Hint

In a circular linked list, the last node's next points back to the first node.

3

Write functions to traverse both linked lists

Write a function called traverseLinear that takes linearHead: Node and returns an array of values by traversing until null. Write another function called traverseCircular that takes circularHead: Node and returns an array of values by traversing nodes until it reaches the start node again (visit each node once).

DSA Typescript

class Node {
    value: number;
    next: Node | null;
    constructor(value: number, next: Node | null = null) {
        this.value = value;
        this.next = next;
    }
}

const node1 = new Node(10);
const node2 = new Node(20);
const node3 = new Node(30);

node1.next = node2;
node2.next = node3;
node3.next = null;

const linearHead = node1;

const cnode1 = new Node(10);
const cnode2 = new Node(20);
const cnode3 = new Node(30);

cnode1.next = cnode2;
cnode2.next = cnode3;
cnode3.next = cnode1;

const circularHead = cnode1;

// Write traverseLinear and traverseCircular functions below
// Your code here

Hint

For linear traversal, stop when current is null. For circular traversal, stop when you reach the start node again.

4

Print the traversal results of both lists

Use console.log to print the result of traverseLinear(linearHead) and traverseCircular(circularHead).

DSA Typescript

class Node {
    value: number;
    next: Node | null;
    constructor(value: number, next: Node | null = null) {
        this.value = value;
        this.next = next;
    }
}

const node1 = new Node(10);
const node2 = new Node(20);
const node3 = new Node(30);

node1.next = node2;
node2.next = node3;
node3.next = null;

const linearHead = node1;

const cnode1 = new Node(10);
const cnode2 = new Node(20);
const cnode3 = new Node(30);

cnode1.next = cnode2;
cnode2.next = cnode3;
cnode3.next = cnode1;

const circularHead = cnode1;

function traverseLinear(linearHead: Node): number[] {
    const values: number[] = [];
    let current: Node | null = linearHead;
    while (current !== null) {
        values.push(current.value);
        current = current.next;
    }
    return values;
}

function traverseCircular(circularHead: Node): number[] {
    const values: number[] = [];
    let current: Node | null = circularHead;
    if (current === null) return values;
    do {
        values.push(current.value);
        current = current.next;
    } while (current !== circularHead && current !== null);
    return values;
}

// Print traversal results below
// Your code here

Hint

Use console.log(traverseLinear(linearHead)) and console.log(traverseCircular(circularHead)) to print the arrays.

Practice

1. What is the main difference between a circular linked list and a linear linked list?

easy

A. In a circular linked list, the last node points back to the first node, forming a circle.

B. In a linear linked list, the last node points back to the first node, forming a circle.

C. A circular linked list has no nodes.

D. A linear linked list always has only one node.

Solution

1. Step 1: Understand node connections in linear linked list

   In a linear linked list, nodes are connected one after another, and the last node points to null, ending the list.

2. Step 2: Understand node connections in circular linked list

   In a circular linked list, the last node points back to the first node, creating a loop or circle.

3. Final Answer:

   In a circular linked list, the last node points back to the first node, forming a circle. -> Option A

4. Quick Check:

   Circular list loops back = In a circular linked list, the last node points back to the first node, forming a circle. [OK]

Hint: Circular loops back to start; linear ends with null [OK]

Common Mistakes:

• Confusing which list loops back
• Thinking linear list forms a circle
• Assuming circular list has no end node

2. Which of the following is the correct way to check if a single-node linked list is circular in TypeScript?

easy

A. if (head.next === 0) { /* linear list */ }

B. if (head.next === null) { /* linear list */ }

C. if (head.next === undefined) { /* circular list */ }

D. if (head.next === head) { /* circular list */ }

Solution

1. Step 1: Understand node pointer in circular list

   In a circular linked list, the next pointer of the last node points back to the head node itself.

2. Step 2: Check the condition for circular list

   If head.next equals head, it means the list loops back to the start, confirming circularity.

3. Final Answer:

   if (head.next === head) { /* circular list */ } -> Option D

4. Quick Check:

   Next points to head means circular [OK]

Hint: Check if next points to head for circular list [OK]

Common Mistakes:

• Checking for null instead of head
• Using undefined instead of null
• Confusing zero with null pointer

3. Consider this TypeScript code for a circular linked list:

class Node {
  value: number;
  next: Node | null;
  constructor(value: number) {
    this.value = value;
    this.next = null;
  }
}

const head = new Node(1);
const second = new Node(2);
const third = new Node(3);

head.next = second;
second.next = third;
third.next = head;

let current = head;
let count = 0;
while (count < 5) {
  console.log(current.value);
  current = current.next!;
  count++;
}

What will be the output printed?

medium

A. 1 2 3 null null

B. 1 2 3 1 2

C. 1 2 3 4 5

D. 1 2 3 3 3

Solution

1. Step 1: Understand the circular linked list structure

   The last node (third) points back to head, so the list loops: 1 -> 2 -> 3 -> 1 -> ...

2. Step 2: Trace the loop for 5 iterations

   Starting at head (1), the values printed are: 1, 2, 3, then loops back to 1, then 2.

3. Final Answer:

   1 2 3 1 2 -> Option B

4. Quick Check:

   Circular list repeats nodes in order [OK]

Hint: Circular list repeats nodes; count controls output length [OK]

Common Mistakes:

• Assuming list ends after 3 nodes
• Printing null after last node
• Confusing node values after loop

4. The following TypeScript code attempts to detect if a linked list is circular but has a bug:

function isCircular(head: Node | null): boolean {
  let current = head;
  while (current !== null) {
    if (current.next === head) {
      return true;
    }
    current = current.next!;
  }
  return false;
}

What is the bug in this code?

medium

A. It incorrectly returns true for linear lists.

B. It does not handle empty lists (head = null).

C. It may enter an infinite loop if the list is circular but not pointing directly to head.

D. It uses 'current.next!' which causes a syntax error.

Solution

1. Step 1: Analyze the loop condition and pointer movement

   The loop moves current to current.next until current is null or current.next equals head.

2. Step 2: Identify the problem with circular lists

   If the list is circular but the loop does not point directly back to head (e.g., cycle in middle), the loop never ends, causing infinite loop.

3. Final Answer:

   It may enter an infinite loop if the list is circular but not pointing directly to head. -> Option C

4. Quick Check:

   Loop may never end if cycle not at head [OK]

Hint: Check for cycles anywhere, not just pointing to head [OK]

Common Mistakes:

• Assuming only last node points to head
• Ignoring infinite loop possibility
• Confusing syntax error with logic error

5. You want to convert a linear linked list into a circular linked list in TypeScript. Given the code below, which line correctly completes the conversion?

class Node {
  value: number;
  next: Node | null;
  constructor(value: number) {
    this.value = value;
    this.next = null;
  }
}

const head = new Node(10);
const second = new Node(20);
const third = new Node(30);

head.next = second;
second.next = third;
third.next = null; // currently linear list

// Which line below makes the list circular?
// A: third.next = null;
// B: second.next = head;
// C: head.next = third;
// D: third.next = head;

medium

A. third.next = head;

B. second.next = head;

C. head.next = third;

D. third.next = null;

Solution

1. Step 1: Understand the current list structure

   The list is linear: head -> second -> third -> null.

2. Step 2: Make the last node point to head to form a circle

   Setting third.next = head connects the last node back to the first, making the list circular.

3. Final Answer:

   third.next = head; -> Option A

4. Quick Check:

   Last node points to head for circular list [OK]

Hint: Last node's next must point to head for circular list [OK]

Common Mistakes:

• Setting next to null keeps list linear
• Pointing head.next to third breaks order
• Pointing second.next to head creates wrong cycle