Traversal of Circular Linked List in DSA Java - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to start traversal from the head node.

DSA Java

Node current = [1];

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

Ahead

Btail

Cnull

Dnext

Attempts:

3 left

💡 Hint

Common Mistakes

Starting traversal from tail instead of head.

Using null as starting point.

Traversal of a circular linked list starts from the head node.

2fill in blank

medium

Complete the code to move to the next node during traversal.

DSA Java

current = current.[1];

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

Anext

Btail

Chead

Dprev

Attempts:

3 left

💡 Hint

Common Mistakes

Using prev instead of next.

Assigning head or tail incorrectly.

To traverse, move to the next node from the current node.

3fill in blank

hard

Fix the error in the loop condition to stop traversal after one full cycle.

DSA Java

while (current != [1]) {
    System.out.print(current.data + " -> ");
    current = current.next;
}
System.out.print(current.data + " -> null");

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

Anull

Btail

Chead

Dcurrent

Attempts:

3 left

💡 Hint

Common Mistakes

Using null as stopping condition in circular list.

Using tail or current incorrectly.

The loop should stop when current reaches the head node again, completing one full cycle.

4fill in blank

hard

Fill both blanks to create a for loop that traverses the circular linked list once.

DSA Java

for (Node current = [1]; current != [2]; current = current.next) {
    System.out.print(current.data + " -> ");
}
System.out.print(current.data + " -> null");

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

Ahead

Btail

Chead.next

Dnull

Attempts:

3 left

💡 Hint

Common Mistakes

Starting from head.next and stopping at head.

Using null as stopping condition.

The loop starts from head and stops when it reaches head.next again, completing one full traversal.

5fill in blank

hard

Fill all three blanks to build a while loop that prints all nodes in the circular linked list once.

DSA Java

Node current = [1];
do {
    System.out.print(current.data + " -> ");
    current = current.[2];
} while (current != [3]);
System.out.print("null");

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

Ahead

Bnext

Dtail

Attempts:

3 left

💡 Hint

Common Mistakes

Using while loop without do causes missing first node.

Stopping condition using tail or null.

Start from head, move to next node each time, and stop when current reaches head again.

Practice

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

easy

A. In a singly linked list, traversal stops when the starting node is reached again.

B. In a circular linked list, traversal stops when the last node's next is null.

C. Traversal is the same for both lists.

D. In a circular linked list, traversal stops when the starting node is reached again.

Solution

1. Step 1: Understand traversal stopping condition for singly linked list

   Traversal stops when the next pointer is null, indicating the end of the list.

2. Step 2: Understand traversal stopping condition for circular linked list

   Traversal stops when the traversal reaches the starting node again, since the list loops back.

3. Final Answer:

   In a circular linked list, traversal stops when the starting node is reached again. -> Option D

4. Quick Check:

   Stopping condition differs: null vs start node [OK]

Hint: Remember circular lists loop back to start node [OK]

Common Mistakes:

• Stopping traversal at null in circular list
• Confusing stopping conditions between list types
• Assuming circular list ends with null pointer

2. Which of the following Java code snippets correctly starts traversal of a circular linked list from the head node?

easy

A. Node current = head; do { System.out.println(current.data); current = current.next; } while(current != head);

B. Node current = head; while(current != null) { System.out.println(current.data); current = current.next; }

C. Node current = head.next; while(current != head) { System.out.println(current.data); current = current.next; }

D. Node current = null; do { System.out.println(current.data); current = current.next; } while(current != head);

Solution

1. Step 1: Check initialization and loop condition

   Node current = head; do { System.out.println(current.data); current = current.next; } while(current != head); initializes current to head and uses a do-while loop to print and move until current equals head again, which is correct for circular lists.

2. Step 2: Analyze other options

   Node current = head; while(current != null) { System.out.println(current.data); current = current.next; } uses while(current != null), which is incorrect for circular lists as next is never null. Node current = head.next; while(current != head) { System.out.println(current.data); current = current.next; } starts from head.next and misses printing head data. Node current = null; do { System.out.println(current.data); current = current.next; } while(current != head); initializes current to null, causing NullPointerException.

3. Final Answer:

   Node current = head; do { System.out.println(current.data); current = current.next; } while(current != head); -> Option A

4. Quick Check:

   Use do-while with current != head [OK]

Hint: Use do-while loop starting at head for circular lists [OK]

Common Mistakes:

• Using while(current != null) for circular lists
• Starting traversal from head.next and missing head node
• Initializing current to null causing errors

3. What will be the output of the following code snippet for a circular linked list with nodes containing data 10 -> 20 -> 30 -> back to 10?

Node head = new Node(10);
head.next = new Node(20);
head.next.next = new Node(30);
head.next.next.next = head;

Node current = head;
do {
    System.out.print(current.data + " ");
    current = current.next;
} while(current != head);

medium

A. 10 20 30 10

B. 10 20 30

C. 20 30 10

D. 10 20 30 30

Solution

1. Step 1: Understand the circular linked list structure

   The list nodes are 10 -> 20 -> 30, and 30 points back to 10, making it circular.

2. Step 2: Trace the do-while loop output

   Starting at head (10), print 10, move to 20, print 20, move to 30, print 30, move to 10 again. Loop stops when current == head, so 10 is not printed again.

3. Final Answer:

   10 20 30 -> Option B

4. Quick Check:

   Print nodes once until back to start [OK]

Hint: Do-while prints all nodes once before stopping [OK]

Common Mistakes:

• Printing the start node twice
• Missing the first node in output
• Printing extra nodes beyond the loop

4. Identify the error in the following code snippet for traversing a circular linked list:

Node current = head;
while(current != head) {
    System.out.print(current.data + " ");
    current = current.next;
}

medium

A. The loop never executes because current == head initially.

B. The loop causes infinite printing of nodes.

C. The code throws NullPointerException.

D. The loop skips the last node.

Solution

1. Step 1: Analyze loop condition with initial current value

   current is initialized to head, so current != head is false at start, loop body never runs.

2. Step 2: Understand correct loop for circular list traversal

   Use do-while loop to ensure at least one iteration, since current starts at head.

3. Final Answer:

   The loop never executes because current == head initially. -> Option A

4. Quick Check:

   while(current != head) false at start [OK]

Hint: Use do-while to run loop at least once [OK]

Common Mistakes:

• Using while instead of do-while for circular lists
• Not printing the first node
• Assuming loop runs when condition false initially

5. Given a circular linked list where each node contains an integer, write a method to find the sum of all node values. Which approach below correctly handles the traversal without infinite loop?

hard

A. Initialize sum=0; Node current=head.next; while(current != head) { sum += current.data; current = current.next; } return sum;

B. Initialize sum=0; Node current=head; while(current != null) { sum += current.data; current = current.next; } return sum;

C. Initialize sum=0; Node current=head; do { sum += current.data; current = current.next; } while(current != head); return sum;

D. Initialize sum=0; Node current=null; do { sum += current.data; current = current.next; } while(current != head); return sum;

Solution

1. Step 1: Understand traversal stopping condition for circular list

   Traversal must stop when current returns to head to avoid infinite loop.

2. Step 2: Analyze each option's traversal logic

   Initialize sum=0; Node current=head; do { sum += current.data; current = current.next; } while(current != head); return sum; uses do-while starting at head, summing all nodes once. Initialize sum=0; Node current=head; while(current != null) { sum += current.data; current = current.next; } return sum; uses while(current != null), which never happens in circular list. Initialize sum=0; Node current=head.next; while(current != head) { sum += current.data; current = current.next; } return sum; starts at head.next, missing head's data. Initialize sum=0; Node current=null; do { sum += current.data; current = current.next; } while(current != head); return sum; initializes current to null causing error.

3. Final Answer:

   Initialize sum=0; Node current=head; do { sum += current.data; current = current.next; } while(current != head); return sum; -> Option C

4. Quick Check:

   Use do-while with current != head for full traversal [OK]

Hint: Sum with do-while loop until current equals head [OK]

Common Mistakes:

• Using while(current != null) causing infinite loop
• Skipping head node in sum calculation
• Initializing current to null causing errors