circularLinkedList.cpp

#include <iostream>
using namespace std;

struct Node
{
  int data;
  Node *next;
  Node(int x)
  {
    data = x;
    next = NULL;
  }
};

// This function returns true if given linked list is circular, else false.
bool isCircular(Node *head)
{
  // If the head is null, the linked list is empty, so it is not circular
  if (!head)
    return false;

  // Traverse the linked list until either the end is reached or the next node is equal to the head
  Node *curr = head;
  while (curr->next && curr->next != head)
    curr = curr->next;

  // If the end is reached before finding the head again, the linked list is not circular
  if (curr->next == NULL)
    return false;

  // If the head is found again before reaching the end, the linked list is circular
  return true;
}

int main()
{
  Node *head = new Node(1);
  head->next = new Node(2);
  head->next->next = new Node(3);
  head->next->next->next = new Node(4);

  isCircular(head) ? cout << "Yes\n" : cout << "No\n";

  // Making linked list circular
  head->next->next->next->next = head;
  isCircular(head) ? cout << "Yes\n" : cout << "No\n";

  return 0;
}