Traversal of Circular Linked List in DSA C - Execution Trace

Concept Flow - Traversal of Circular Linked List

Start at head node

↓

Visit current node and process data

↓

Move to next node

↓

Check if current node is head again?

No→Repeat visit and move

Yes↓

Stop traversal

Start from the head node, visit each node, move to the next, and stop when you return to the head.

Execution Sample

DSA C

Node* current = head;
do {
    printf("%d -> ", current->data);
    current = current->next;
} while (current != head);

Prints all nodes in the circular linked list starting from head until it loops back.

Execution Table

Step	Operation	Current Node Data	Pointer Changes	Visual State
1	Start at head	10	current = head (10)	10 -> 20 -> 30 -> 40 -> (back to 10)
2	Print current data	10	No pointer change	10 -> 20 -> 30 -> 40 -> (back to 10)
3	Move to next node	20	current = current->next (20)	10 -> 20 -> 30 -> 40 -> (back to 10)
4	Print current data	20	No pointer change	10 -> 20 -> 30 -> 40 -> (back to 10)
5	Move to next node	30	current = current->next (30)	10 -> 20 -> 30 -> 40 -> (back to 10)
6	Print current data	30	No pointer change	10 -> 20 -> 30 -> 40 -> (back to 10)
7	Move to next node	40	current = current->next (40)	10 -> 20 -> 30 -> 40 -> (back to 10)
8	Print current data	40	No pointer change	10 -> 20 -> 30 -> 40 -> (back to 10)
9	Move to next node	10	current = current->next (10)	10 -> 20 -> 30 -> 40 -> (back to 10)
10	Check if current == head	10	Condition true, stop traversal	Traversal complete

💡 Traversal stops when current pointer returns to head node.

Variable Tracker

Variable	Start	After Step 3	After Step 5	After Step 7	After Step 9	Final
current	head (10)	20	30	40	10	10 (stop)

Key Moments - 3 Insights

Why do we use a do-while loop instead of a while loop?

Because we must visit the head node at least once before checking if we returned to it, as shown in steps 1 and 2 where current starts at head and prints before condition check.

What happens if the list has only one node?

The traversal prints that single node once and stops immediately after moving back to head, similar to step 9 where current returns to head and traversal ends.

Why does traversal stop when current equals head again?

Because in a circular list, returning to head means we completed a full cycle, so continuing would repeat nodes endlessly, as shown in step 10 where condition current == head is true and traversal stops.

Visual Quiz - 3 Questions

Look at the execution table, what is the value of 'current' after step 5?

A 30

B 40

C 20

D 10

💡 Hint

Check the 'Pointer Changes' column at step 5 in the execution table.

At which step does the traversal detect it has completed a full cycle?

A Step 9

B Step 10

C Step 8

D Step 7

💡 Hint

Look for the step where 'Check if current == head' is true in the execution table.

If the circular linked list had only one node with data 10, how many times would the data print?

A Twice

B Zero times

C Once

D Infinite times

💡 Hint

Refer to the key moment about single-node list traversal.

Concept Snapshot

Traversal of Circular Linked List:
- Start at head node
- Visit and process current node
- Move to next node
- Stop when current returns to head
- Use do-while loop to ensure head is processed
- Prevent infinite loops by checking current == head

Full Transcript

Traversal of a circular linked list starts at the head node. We visit the current node and process its data, then move to the next node. This repeats until we return to the head node, indicating a full cycle. A do-while loop is used to ensure the head node is visited before checking the stopping condition. This prevents infinite loops and ensures all nodes are processed exactly once. If the list has only one node, it prints once and stops immediately after returning to head.

Practice

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

easy

A. In a circular linked list, traversal stops at the last node with NULL next pointer.

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

C. In a circular linked list, traversal requires a double pointer.

D. In a circular linked list, traversal is done only once regardless of nodes.

Solution

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

   In a singly linked list, traversal stops when the next pointer is NULL, indicating the end.

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

   In a circular linked list, there is no NULL next pointer; traversal stops when the starting node is reached again.

3. Final Answer:

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

4. Quick Check:

   Traversal stops at start node in circular list [OK]

Hint: Stop traversal when you reach the start node again [OK]

Common Mistakes:

• Assuming NULL marks end in circular list
• Stopping traversal too early
• Confusing circular with doubly linked list
• Not checking for start node to stop

2. Which of the following is the correct syntax to start traversal from the head node in a circular linked list in C?

easy

A. Node* temp = head; for(int i=0; inext; }

B. Node* temp = head; while(temp != NULL) { /* process temp */ temp = temp->next; }

C. Node* temp = head; do { /* process temp */ temp = temp->next; } while(temp != head);

D. Node* temp = head; while(temp->next != NULL) { /* process temp */ temp = temp->next; }

Solution

1. Step 1: Identify correct loop structure for circular linked list traversal

   Traversal must start at head and continue until we reach head again, so do-while loop is suitable.

2. Step 2: Check each option's loop condition

   Node* temp = head; do { /* process temp */ temp = temp->next; } while(temp != head); uses do-while with condition temp != head, which correctly traverses all nodes once.

3. Final Answer:

   Node* temp = head; do { /* process temp */ temp = temp->next; } while(temp != head); -> Option C

4. Quick Check:

   Use do-while with temp != head for circular list [OK]

Hint: Use do-while loop to traverse circular linked list [OK]

Common Mistakes:

• Using while(temp != NULL) in circular list
• Using for loop without length variable
• Checking temp->next != NULL which never happens
• Starting traversal without processing head

3. What will be the output of the following C code snippet for a circular linked list with nodes containing values 10, 20, 30?

Node* temp = head;
do {
    printf("%d ", temp->data);
    temp = temp->next;
} while(temp != head);

medium

A. 10 20 30

B. 10 20 30 10

C. 20 30 10

D. 10 20

Solution

1. Step 1: Understand traversal order in circular linked list

   Traversal starts at head (10), prints data, moves to next node until it reaches head again.

2. Step 2: Trace the loop execution

   Prints 10, moves to 20, prints 20, moves to 30, prints 30, moves back to 10, loop ends.

3. Final Answer:

   10 20 30 -> Option A

4. Quick Check:

   Print nodes once until back to head [OK]

Hint: Print nodes until you reach start node again [OK]

Common Mistakes:

• Printing extra 10 at end
• Starting from second node
• Stopping before last node
• Confusing circular with linear list output

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

Node* temp = head;
while(temp != NULL) {
    printf("%d ", temp->data);
    temp = temp->next;
    if(temp == head) break;
}

medium

A. The loop condition while(temp != NULL) is wrong for circular lists.

B. The break condition is incorrect; it should check temp->next.

C. The loop condition should be do-while, not while.

D. The printf statement should be after updating temp.

Solution

1. Step 1: Analyze loop condition for circular linked list

   In circular linked list, next pointer is never NULL, so while(temp != NULL) will cause infinite loop.

2. Step 2: Check break condition usage

   Break condition temp == head is correct to stop traversal after full cycle.

3. Final Answer:

   The loop condition while(temp != NULL) is wrong for circular lists. -> Option A

4. Quick Check:

   Use do-while or check for start node, not NULL [OK]

Hint: Never check NULL in circular list traversal [OK]

Common Mistakes:

• Using while(temp != NULL) causing infinite loop
• Incorrect break condition
• Printing after moving temp
• Confusing linear and circular list traversal

5. You have a circular linked list with nodes containing values 5, 15, 25, 35. You want to print all nodes except the node with value 25 during traversal. Which modification to the traversal code below achieves this?

Node* temp = head;
do {
    // print temp->data
    temp = temp->next;
} while(temp != head);

hard

A. Start traversal from node after 25.

B. Skip the node by setting temp->next = temp->next->next when temp->data == 25.

C. Break the loop when temp->data == 25.

D. Add an if condition: if(temp->data != 25) printf("%d ", temp->data);

Solution

1. Step 1: Understand requirement to skip printing node with value 25

   We want to traverse all nodes but not print the node with data 25.

2. Step 2: Modify printing logic inside traversal loop

   Add an if condition to print only if temp->data is not 25, so node is visited but not printed.

3. Final Answer:

   Add an if condition: if(temp->data != 25) printf("%d ", temp->data); -> Option D

4. Quick Check:

   Use if condition to skip printing specific node [OK]

Hint: Use if condition inside loop to skip unwanted node [OK]

Common Mistakes:

• Modifying links during traversal causing list corruption
• Breaking loop early missing nodes
• Starting traversal from wrong node
• Printing all nodes without condition