GFG_CheckCircularLinkedList.cpp

/* https://practice.geeksforgeeks.org/problems/circular-linked-list/1#
 * Given head, the head of a singly linked list, find if the linked list is circular or not.
 * A linked list is called circular if it not NULL terminated and all nodes are connected in the form of a cycle.
 * An empty linked list is considered as circular.
 */

// { Driver Code Starts
// C program to find n'th Node in linked list
#include <stdio.h>
#include <stdlib.h>
#include<iostream>
using namespace std;

/* Link list Node */
struct Node
{
    int data;
    struct Node* next;

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

};


/* Function to get the middle of the linked list*/
bool isCircular(struct Node *head);

/* Driver program to test above function*/
int main()
{
    int T,i,n,l,k;

    cin>>T;

    while(T--){

        cin>>n>>k;
        Node *head=NULL, *tail = NULL;
        int x;
        cin >> x;
        head = new Node(x);
        tail = head;
        for(int i=0;i<n-1;i++)
        {
            cin>>x;
            tail -> next = new Node(x);
            tail = tail -> next;
        }
        if (k==1 && n >= 1)
            tail->next = head;


        printf("%d\n", isCircular(head));
    }
    return 0;
}

// } Driver Code Ends


/* Link list Node
struct Node
{
    int data;
    struct Node* next;

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

};
*/

/* Should return true if linked list is circular, else false */
bool isCircular(Node *head)
{
    Node* ptr = head->next;
    while(ptr!=head && ptr!=nullptr)
        ptr=ptr->next;

    if(ptr == head) return true;
    else return false;
}