Traversal of Circular Linked List in DSA C - Build from Scratch

Traversal of Circular Linked List

📖 Scenario: Imagine you have a circular queue of people waiting in a circle. You want to visit each person exactly once and say hello. This is like traversing a circular linked list where the last person points back to the first.

🎯 Goal: You will create a circular linked list with three nodes, then write code to traverse it and print each node's data exactly once.

📋 What You'll Learn

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

Set up a pointer to start traversal from the head node

Write a loop to traverse the circular linked list and print each node's data once

Print the data values separated by spaces on one line

💡 Why This Matters

🌍 Real World

Circular linked lists are used in real-world applications like round-robin scheduling, multiplayer games where players take turns in a circle, and buffering data streams.

💼 Career

Understanding circular linked lists helps in system programming, game development, and designing efficient data structures for continuous looping tasks.

1

Create a circular linked list with three nodes

Create three nodes called node1, node2, and node3 of type struct Node. Assign node1->data = 10, node2->data = 20, and node3->data = 30. Link them so that node1->next = node2, node2->next = node3, and node3->next = node1 to form a circular linked list.

DSA C

#include 
#include 

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

int main() {
    // Create three nodes and link them circularly
    // Your code here

    return 0;
}

Hint

Use malloc to create nodes and set their data and next pointers to form a circle.

2

Set a pointer to the head node for traversal

Create a pointer called current and set it to point to node1 to start traversal from the head of the circular linked list.

DSA C

#include 
#include 

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

int main() {
    struct Node* node1 = (struct Node*)malloc(sizeof(struct Node));
    struct Node* node2 = (struct Node*)malloc(sizeof(struct Node));
    struct Node* node3 = (struct Node*)malloc(sizeof(struct Node));

    node1->data = 10;
    node2->data = 20;
    node3->data = 30;

    node1->next = node2;
    node2->next = node3;
    node3->next = node1;

    // Set current pointer to node1
    // Your code here

    return 0;
}

Hint

Use a pointer variable current to start at the head node node1.

3

Traverse the circular linked list and print each node's data

Write a do-while loop that prints current->data followed by a space, then moves current to current->next. Continue looping until current is again node1 to ensure each node is printed exactly once.

DSA C

#include 
#include 

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

int main() {
    struct Node* node1 = (struct Node*)malloc(sizeof(struct Node));
    struct Node* node2 = (struct Node*)malloc(sizeof(struct Node));
    struct Node* node3 = (struct Node*)malloc(sizeof(struct Node));

    node1->data = 10;
    node2->data = 20;
    node3->data = 30;

    node1->next = node2;
    node2->next = node3;
    node3->next = node1;

    struct Node* current = node1;

    // Traverse and print data
    // Your code here

    return 0;
}

Hint

Use a do-while loop to print each node's data and move to the next node until you return to the start.

4

Print the traversal output

Add a printf statement to print a newline character \n after the traversal loop to end the output cleanly.

DSA C

#include 
#include 

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

int main() {
    struct Node* node1 = (struct Node*)malloc(sizeof(struct Node));
    struct Node* node2 = (struct Node*)malloc(sizeof(struct Node));
    struct Node* node3 = (struct Node*)malloc(sizeof(struct Node));

    node1->data = 10;
    node2->data = 20;
    node3->data = 30;

    node1->next = node2;
    node2->next = node3;
    node3->next = node1;

    struct Node* current = node1;

    do {
        printf("%d ", current->data);
        current = current->next;
    } while (current != node1);

    // Print newline
    // Your code here

    return 0;
}

Hint

Use printf("\n") to print a newline after the loop.

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