Circular vs Linear Linked List Key Difference in DSA C++ - Interactive Comparison Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a linear linked list node pointing to null.

DSA C++

struct Node {
    int data;
    Node* next = [1];
};

Drag options to blanks, or click blank then click option'

A0

Bnullptr

Cthis

DNULL

Attempts:

3 left

💡 Hint

Common Mistakes

Using 0 or NULL instead of nullptr

Using 'this' pointer incorrectly

In modern C++, nullptr is used to indicate the end of a linear linked list.

2fill in blank

medium

Complete the code to make the last node point back to the head, forming a circular linked list.

DSA C++

void makeCircular(Node* last, Node* head) {
    last->next = [1];
}

Drag options to blanks, or click blank then click option'

Ahead

Bnullptr

Clast

DNULL

Attempts:

3 left

💡 Hint

Common Mistakes

Pointing last->next to nullptr or NULL

Pointing last->next to itself

In a circular linked list, the last node points back to the head node.

3fill in blank

hard

Fix the error in the loop condition to traverse a circular linked list correctly.

DSA C++

void traverseCircular(Node* head) {
    Node* temp = head;
    do {
        std::cout << temp->data << " -> ";
        temp = temp->next;
    } while (temp != [1]);
    std::cout << "null";
}

Drag options to blanks, or click blank then click option'

Anullptr

Btemp

Chead

Dlast

Attempts:

3 left

💡 Hint

Common Mistakes

Using nullptr as stop condition

Using temp instead of head

In circular linked list traversal, stop when you reach the head again.

4fill in blank

hard

Fill both blanks to create a linear linked list and check if it is circular.

DSA C++

bool isCircular(Node* head) {
    if (head == [1]) return false;
    Node* temp = head->next;
    while (temp != [2] && temp != nullptr) {
        temp = temp->next;
    }
    return temp == head;
}

Drag options to blanks, or click blank then click option'

Anullptr

Bhead

Clast

DNULL

Attempts:

3 left

💡 Hint

Common Mistakes

Using head in first blank

Using nullptr in second blank

Check if head is null first, then traverse until you find head again or reach null.

5fill in blank

hard

Fill all three blanks to insert a new node at the end of a circular linked list.

DSA C++

void insertEnd(Node*& head, int value) {
    Node* newNode = new Node{value, [1];
    if (head == [2]) {
        head = newNode;
        newNode->next = newNode;
    } else {
        Node* temp = head;
        while (temp->next != [3]) {
            temp = temp->next;
        }
        temp->next = newNode;
        newNode->next = head;
    }
}

Drag options to blanks, or click blank then click option'

Anullptr

Chead

Attempts:

3 left

💡 Hint

Common Mistakes

Setting newNode->next to head initially

Checking head == head instead of nullptr

Using nullptr instead of head in while condition

New node initially points to nullptr. If list empty (head is nullptr), set head to new node and point new node to itself. Otherwise, find last node (where next points to head) and insert new node there.

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, while in a linear linked list, the last node points to null.

B. A circular linked list stores data in a circle shape, while a linear linked list stores data in a straight line.

C. Circular linked lists can only store numbers, while linear linked lists can store any data type.

D. Linear linked lists have nodes connected randomly, while circular linked lists have nodes connected sequentially.

Solution

1. Step 1: Understand the structure of a linear linked list

   A linear linked list has nodes connected one after another, and the last node points to null, indicating the end.

2. Step 2: Understand the structure of a circular linked list

   In a circular linked list, the last node points back to the first node, forming a circle with no null end.

3. Final Answer:

   In a circular linked list, the last node points back to the first node, while in a linear linked list, the last node points to null. -> Option A

4. Quick Check:

   Last node points to first node = circular linked list [OK]

Hint: Last node points to null in linear, to head in circular [OK]

Common Mistakes:

• Thinking circular lists store data in a circle shape physically
• Confusing data types allowed in each list
• Assuming linear lists have random connections

2. Which of the following is the correct way to check if a linked list is circular in C++?

easy

A. while (head != nullptr) head = head->next; return true;

B. if (head->next == nullptr) return true;

C. if (head == nullptr) return false;

D. Node* temp = head; while (temp != nullptr && temp->next != head) temp = temp->next; return (temp != nullptr && temp->next == head);

Solution

1. Step 1: Understand the logic to detect circular linked list

   We traverse nodes until we find a node whose next points back to head or reach null.

2. Step 2: Analyze the given code snippets

   Node* temp = head; while (temp != nullptr && temp->next != head) temp = temp->next; return (temp != nullptr && temp->next == head); correctly traverses nodes and checks if the next pointer points to head, indicating circularity.

3. Final Answer:

   Node* temp = head; while (temp != nullptr && temp->next != head) temp = temp->next; return (temp != nullptr && temp->next == head); -> Option D

4. Quick Check:

   Traverse until next points to head = circular check [OK]

Hint: Traverse until next points to head to confirm circular [OK]

Common Mistakes:

• Checking only if head is null
• Assuming next == nullptr means circular
• Infinite loop by not checking null condition

3. What will be the output of the following C++ code snippet?

struct Node {
  int data;
  Node* next;
};

Node* head = new Node{1, nullptr};
head->next = new Node{2, nullptr};
head->next->next = head; // circular link

Node* temp = head;
int count = 0;
while (temp != nullptr && count < 4) {
  std::cout << temp->data << " ";
  temp = temp->next;
  count++;
}

medium

A. 1 2 1 2

B. 1 2 3 4

C. 1 2

D. 1 2 1 2 1

Solution

1. Step 1: Understand the linked list structure

   Node 1 points to Node 2, and Node 2 points back to Node 1, making it circular.

2. Step 2: Trace the loop output

   The loop prints data 4 times: 1, 2, 1, 2, then stops because count reaches 4.

3. Final Answer:

   1 2 1 2 -> Option A

4. Quick Check:

   Print 4 nodes in circular list = 1 2 1 2 [OK]

Hint: Count limits output in circular list traversal [OK]

Common Mistakes:

• Assuming next nullptr ends loop
• Expecting 3 or 4 as data values
• Not limiting loop count causing infinite print

4. Identify the error in the following code that attempts to create a circular linked list:

struct Node {
  int data;
  Node* next;
};

Node* head = new Node{10, nullptr};
head->next = new Node{20, nullptr};
head->next->next = nullptr; // supposed to be circular

medium

A. The head node should not be initialized with nullptr.

B. The last node's next pointer should point to head, not nullptr.

C. The data values 10 and 20 are invalid for circular lists.

D. The Node struct is missing a previous pointer.

Solution

1. Step 1: Review the code's intention

   The code tries to create a circular linked list but sets the last node's next to nullptr.

2. Step 2: Identify the correct pointer for circular list

   In a circular linked list, the last node's next must point back to the head node, not nullptr.

3. Final Answer:

   The last node's next pointer should point to head, not nullptr. -> Option B

4. Quick Check:

   Last node next = head for circular list [OK]

Hint: Last node next must link to head in circular list [OK]

Common Mistakes:

• Leaving last node next as nullptr
• Confusing circular with doubly linked list
• Thinking data values affect circularity

5. You have a circular linked list where each node contains an integer. Write a C++ function to count the number of nodes in the list without using extra memory. What is the key difference in traversal compared to a linear linked list?

hard

A. Traverse until the current node is null.

B. Traverse until the current node's next is null.

C. Traverse until the current node returns to the head node.

D. Traverse until a fixed number of nodes is reached.

Solution

1. Step 1: Understand traversal in linear linked list

   In a linear linked list, traversal stops when the current node is null (end of list).

2. Step 2: Understand traversal in circular linked list

   In a circular linked list, traversal stops when the current node comes back to the head node, completing the circle.

3. Final Answer:

   Traverse until the current node returns to the head node. -> Option C

4. Quick Check:

   Stop when node loops back to head in circular list [OK]

Hint: Stop traversal when node equals head in circular list [OK]

Common Mistakes:

• Stopping traversal at null in circular list
• Using fixed count without knowing list size
• Confusing next pointer null check with circular condition