Create a Circular Singly Linked List in DSA Java - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a Circular Singly Linked List?

A Circular Singly Linked List is a linked list where the last node points back to the first node, forming a circle. There is no null at the end.

beginner

How do you identify the last node in a Circular Singly Linked List?

The last node is the one whose next pointer points back to the head (first node) instead of null.

intermediate

Why is a Circular Singly Linked List useful compared to a regular singly linked list?

It allows continuous traversal from any node without stopping, useful for applications like round-robin scheduling or buffering.

beginner

In Java, what is the key step to create a circular link after adding the first node?

Set the next pointer of the first node to point to itself, making it circular even with one node.

intermediate

What happens if you forget to update the last node's next pointer to the head in a circular singly linked list?

The list will not be circular; traversal will end at null, losing the circular property.

In a Circular Singly Linked List, what does the last node's next pointer point to?

A Itself

B The head node

C Null

D A random node

The last node's next pointer points back to the head node, making the list circular.

What is the first step when creating a Circular Singly Linked List with one node?

A Set node's next to head's next

B Set node's next to null

C Set node's next to a new node

D Set node's next to itself

For one node, its next pointer must point to itself to form a circular list.

Which of these is NOT a benefit of Circular Singly Linked Lists?

A Faster random access by index

B No need to check for null to end traversal

C Simplifies round-robin scheduling

D Easy continuous traversal

Circular lists do not provide faster random access; they still require traversal.

How do you add a new node at the end of a Circular Singly Linked List?

A Insert node and set last node's next to new node, new node's next to head

B Insert node and set its next to null

C Insert node and set new node's next to last node

D Insert node and set head's next to new node

The new node's next points to head, and the old last node's next points to the new node.

What happens if you traverse a Circular Singly Linked List without a stopping condition?

A Traversal ends at null

B Traversal skips nodes

C Traversal loops infinitely

D Traversal throws an error

Because the list is circular, traversal without a stop condition loops forever.

Explain how to create a Circular Singly Linked List starting from an empty list.

Think about how the last node always points back to the first node.

Describe the key differences between a regular singly linked list and a circular singly linked list.

Focus on the last node's next pointer and traversal behavior.

Practice

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

easy

A. In a circular singly linked list, nodes have two pointers instead of one.

B. In a circular singly linked list, nodes are stored in an array.

C. In a circular singly linked list, the last node points back to the first node.

D. In a circular singly linked list, the first node points to null.

Solution

1. Step 1: Understand the structure of a regular singly linked list

   A regular singly linked list has nodes where each node points to the next node, and the last node points to null.

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

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

3. Final Answer:

   In a circular singly linked list, the last node points back to the first node. -> Option C

4. Quick Check:

   Last node points to first node = B [OK]

Hint: Remember: circular means last node links back to start [OK]

Common Mistakes:

• Thinking circular means nodes have two pointers
• Confusing circular list with doubly linked list
• Assuming last node points to null

2. Which of the following is the correct way to create a new node in Java for a circular singly linked list?

easy

A. Node newNode = new Node(); newNode.next = newNode;

B. Node newNode = new Node(data); newNode.next = null;

C. Node newNode = new Node(); newNode.data = data; newNode.next = null;

D. Node newNode = new Node(data); newNode.next = newNode;

Solution

1. Step 1: Understand node creation for circular singly linked list

   When creating a single node in a circular singly linked list, its next pointer should point to itself to form a circle.

2. Step 2: Check each option

   Node newNode = new Node(data); newNode.next = newNode; sets newNode.next = newNode, which correctly points the node to itself. Other options set next to null or do not initialize properly.

3. Final Answer:

   Node newNode = new Node(data); newNode.next = newNode; -> Option D

4. Quick Check:

   Node points to itself when alone = A [OK]

Hint: Single node's next points to itself in circular list [OK]

Common Mistakes:

• Setting next to null for single node
• Not initializing next pointer
• Confusing syntax for node creation

3. What will be the output of the following code snippet that creates a circular singly linked list with two nodes and prints their data?

class Node {
  int data;
  Node next;
  Node(int d) { data = d; next = null; }
}

public class Test {
  public static void main(String[] args) {
    Node head = new Node(10);
    Node second = new Node(20);
    head.next = second;
    second.next = head;

    System.out.print(head.data + " -> " + head.next.data + " -> " + head.next.next.data);
  }
}

medium

A. 10 -> 20 -> 10

B. 10 -> 20 -> null

C. 10 -> 20 -> 20

D. Compilation error

Solution

1. Step 1: Trace the node connections

   head.data = 10, head.next = second (data 20), second.next = head (data 10), forming a circle.

2. Step 2: Evaluate the print statement

   head.data = 10, head.next.data = 20, head.next.next.data = second.next.data = head.data = 10.

3. Final Answer:

   10 -> 20 -> 10 -> Option A

4. Quick Check:

   Circle repeats first node data = 10 -> 20 -> 10 [OK]

Hint: Follow next pointers carefully to see the cycle [OK]

Common Mistakes:

• Assuming next.next is null
• Confusing node data values
• Expecting compilation error

4. Identify the error in the following code that tries to insert a new node at the end of a circular singly linked list:

public void insertEnd(Node head, int data) {
  Node newNode = new Node(data);
  if (head == null) {
    head = newNode;
    newNode.next = head;
  } else {
    Node temp = head;
    while (temp.next != null) {
      temp = temp.next;
    }
    temp.next = newNode;
    newNode.next = head;
  }
}

medium

A. The while loop condition should check for temp.next != head instead of null.

B. The newNode.next should be set to null instead of head.

C. The head should be updated to newNode after insertion.

D. The method should return the new head node.

Solution

1. Step 1: Understand circular list traversal

   In a circular singly linked list, the last node's next points to head, not null.

2. Step 2: Analyze the while loop condition

   The loop checks temp.next != null, which never happens in circular list; it should check temp.next != head to find the last node.

3. Final Answer:

   The while loop condition should check for temp.next != head instead of null. -> Option A

4. Quick Check:

   Loop must stop at last node pointing to head = A [OK]

Hint: In circular list, last node points to head, not null [OK]

Common Mistakes:

• Using null to detect end in circular list
• Not updating newNode.next correctly
• Ignoring head update when list is empty

5. You want to create a circular singly linked list from an array of integers {5, 10, 15} by inserting nodes at the end. Which sequence of next pointers correctly represents the final circular list?

hard

A. 15 -> 10 -> 5 -> 15

B. 5 -> 10 -> 15 -> 5

C. 5 -> 10 -> 15 -> null

D. 5 -> 15 -> 10 -> 5

Solution

1. Step 1: Insert nodes at end in given order

   Insert 5 first, then 10 at end, then 15 at end, preserving order: 5, 10, 15.

2. Step 2: Set last node's next to head

   After insertion, last node (15) points back to head (5), making the list circular.

3. Final Answer:

   5 -> 10 -> 15 -> 5 -> Option B

4. Quick Check:

   Order preserved, last points to first = C [OK]

Hint: Insert at end keeps order; last node points to first [OK]

Common Mistakes:

• Assuming last node points to null
• Reversing insertion order
• Mixing node data order