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

Traversal of Circular Linked List

📖 Scenario: You are working on a music playlist app. The songs are arranged in a circular linked list so that after the last song, the playlist starts again from the first song.You want to print all the song names in the playlist once, starting from the first song.

🎯 Goal: Build a circular linked list with 3 songs and write code to traverse and print all song names exactly once.

📋 What You'll Learn

Create a circular linked list with exactly 3 nodes

Each node must store a song name as a string

Traverse the circular linked list starting from the head node

Print all song names in order, separated by ' -> ', ending with ' -> null'

💡 Why This Matters

🌍 Real World

Circular linked lists are used in applications like music playlists, round-robin scheduling, and games where the list loops back to the start.

💼 Career

Understanding circular linked lists helps in software development roles involving data structures, system design, and algorithm optimization.

1

Create nodes for the circular linked list

Create a struct called Node with a string member song and a Node* member next. Then create three Node objects named node1, node2, and node3 with song names "SongA", "SongB", and "SongC" respectively.

DSA C++

// Your code here

Hint

Define the Node struct first. Then create three nodes with the given song names and set their next pointers to nullptr for now.

2

Link nodes to form a circular linked list

Link the nodes so that node1.next points to node2, node2.next points to node3, and node3.next points back to node1 to complete the circle. Also, create a pointer head that points to node1.

DSA C++

// Link the nodes to form a circle and create a head pointer
// Your code here

Hint

Set each node's next pointer to the next node, and make the last node point back to the first node. Then create a head pointer to the first node.

3

Traverse the circular linked list

Write a Node* pointer current initialized to head. Use a do-while loop to traverse the circular linked list. Inside the loop, print the current node's song followed by " -> ". Move current to current->next. Stop the loop when current is again equal to head.

DSA C++

// Traverse the circular linked list and print song names
// Your code here

Hint

Use a do-while loop to ensure the loop runs at least once. Print the song name and move to the next node until you come back to the head.

4

Print the end of traversal

After the loop, print "null" to indicate the end of the traversal.

DSA C++

// Print "null" after traversal
// Your code here

Hint

After the loop finishes, print "null" to show the end of the list.

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 pointer.

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

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

D. In a circular linked list, traversal is done backwards only.

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, the last node points back to the first node, so traversal stops when we reach the starting node again to avoid infinite loop.

3. Final Answer:

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

4. Quick Check:

   Traversal stops at start node in circular list = B [OK]

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

Common Mistakes:

• Stopping traversal at NULL pointer in circular list
• Not checking for start node to end traversal
• Assuming circular list traversal is backward

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

easy

A. do { /* process node */ head = head->next; } while(head != NULL);

B. do { /* process node */ head = head->next; } while(head != start);

C. while(head != NULL) { /* process node */ head = head->next; }

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

Solution

1. Step 1: Identify traversal loop type for circular linked list

   Traversal must use a do-while loop to process the start node before checking the condition.

2. Step 2: Check loop condition for circular list traversal

   The loop continues until the pointer returns to the start node, not NULL.

3. Final Answer:

   do { /* process node */ head = head->next; } while(head != start); -> Option B

4. Quick Check:

   Use do-while and check for start node to traverse circular list [OK]

Hint: Use do-while and check for start node, not NULL [OK]

Common Mistakes:

• Using while loop with NULL condition
• Using for loop with NULL condition
• Not processing the start node before condition check

3. What will be the output of the following C++ code that traverses a circular linked list?

#include <iostream>

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

int main() {
  Node n1{1, nullptr}, n2{2, nullptr}, n3{3, nullptr};
  n1.next = &n2;
  n2.next = &n3;
  n3.next = &n1; // circular link

  Node* temp = &n1;
  do {
    std::cout << temp->data << " ";
    temp = temp->next;
  } while(temp != &n1);
  return 0;
}

medium

A. 1 2 3

B. 1 2 3 1

C. 1 2

D. Runtime error

Solution

1. Step 1: Understand the circular linked list structure

   Nodes 1, 2, 3 are linked circularly: 1->2->3->1.

2. Step 2: Trace the do-while traversal

   Traversal starts at node 1, prints 1, moves to 2, prints 2, moves to 3, prints 3, then moves back to 1 and stops.

3. Final Answer:

   1 2 3 -> Option A

4. Quick Check:

   Print nodes until back to start = 1 2 3 [OK]

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

Common Mistakes:

• Printing the start node twice
• Stopping traversal early
• Confusing circular with NULL-terminated list

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

Node* temp = head;
while(temp != head) {
  std::cout << temp->data << " ";
  temp = temp->next;
}

medium

A. The loop misses printing the last node.

B. The loop causes infinite printing of nodes.

C. The code will cause a segmentation fault.

D. The loop never executes because condition is false initially.

Solution

1. Step 1: Analyze the loop condition and initialization

   temp is initialized to head, but the loop condition is while(temp != head), which is false at start.

2. Step 2: Understand loop execution

   Since condition is false initially, the loop body never executes and no nodes are printed.

3. Final Answer:

   The loop never executes because condition is false initially. -> Option D

4. Quick Check:

   temp == head at start, so while(temp != head) is false [OK]

Hint: Use do-while to process start node first in circular list [OK]

Common Mistakes:

• Using while instead of do-while for circular list
• Not processing the start node
• Assuming loop runs at least once

5. Given a circular linked list where each node contains an integer, write a C++ function to find the sum of all node values. Which approach correctly handles the circular nature without infinite loops?

hard

A. Use a do-while loop starting at head, add node data, move to next, stop when back at head.

B. Use a while loop with condition temp != nullptr to sum nodes.

C. Use a for loop from 0 to size-1, summing nodes by moving next pointer.

D. Use recursion without base case to sum nodes.

Solution

1. Step 1: Understand circular list traversal for summation

   Traversal must start at head and continue until we return to head to avoid infinite loops.

2. Step 2: Evaluate each option's approach

   Use a do-while loop starting at head, add node data, move to next, stop when back at head. uses do-while loop checking for return to head, correctly summing all nodes once. Use a while loop with condition temp != nullptr to sum nodes. uses nullptr which never occurs in circular list. Use a for loop from 0 to size-1, summing nodes by moving next pointer. assumes size known but size is not given. Use recursion without base case to sum nodes. causes infinite recursion without base case.

3. Final Answer:

   Use a do-while loop starting at head, add node data, move to next, stop when back at head. -> Option A

4. Quick Check:

   Do-while with head check sums circular list correctly [OK]

Hint: Use do-while and stop when pointer returns to head [OK]

Common Mistakes:

• Using nullptr condition in circular list
• Assuming known size without given data
• Using recursion without base case