Traversal of Circular Linked List in DSA C++ - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a circular linked list?

A circular 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 know when to stop traversing a circular linked list?

You stop when you reach the starting node again after moving forward. This means you have visited all nodes once.

intermediate

Why can't you use 'nullptr' to stop traversal in a circular linked list?

Because the last node points back to the first node, there is no nullptr to mark the end. You must check if you returned to the start node.

beginner

Show the basic steps to traverse a circular linked list starting from head.

1. Start at head node.
2. Visit current node.
3. Move to next node.
4. Repeat until current node is head again.

intermediate

What happens if you forget to check for the start node during traversal?

You will enter an infinite loop because the list is circular and never ends with nullptr.

In a circular linked list, what does the last node point to?

A Itself

B nullptr

C A random node

D The first node

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

When traversing a circular linked list, how do you know when to stop?

A When current node is nullptr

B After 10 nodes

C When current node is the head node again

D When current node's next is nullptr

Traversal stops when you reach the head node again, indicating a full circle.

What is the risk if you forget to check for the head node during traversal?

A You might loop infinitely

B You might get nullptr error

C You might skip nodes

D You might delete nodes accidentally

Without checking for the head node, traversal never ends and causes an infinite loop.

Which of these is NOT true about circular linked lists?

A They have no nullptr at the end

B They end with a nullptr pointer

C They always have a head node

D They can be traversed starting from any node

Circular linked lists do not end with nullptr; the last node points back to the first node.

What is the first step in traversing a circular linked list?

A Set current node to head

B Set current node to random node

C Set current node to last node

D Set current node to nullptr

Traversal starts at the head node.

Explain how to traverse a circular linked list and how to avoid infinite loops.

Think about the circle shape and how to know when you completed one full round.

Describe the difference between traversing a normal linked list and a circular linked list.

Focus on how the end of the list is marked in each case.

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