Check if two Circular Linked Lists are identical

Last Updated : 06 Mar, 2023

Given two circular linked lists L1 and L2, the task is to find if the two circular linked lists are identical or not.

Note: Head of any linked list points to any node of the respective linked list and the lists can contain duplicate elements.

Examples:

Input: L1: 1 -> 2 -> 3 -> 4 -> 5 -> 1 -> 2 -> 6
L2: 5 -> 1 -> 2 -> 6 -> 1 -> 2 -> 3 -> 4
Output: Identical
Explanation: If checked the 5th element of L1 and 1st element of L2 then they are identical.
As they are circular, does not matter from where we start checking.

Input: L1: 1 -> 2 -> 3
L2: 1 ->3 -> 2
Output: Not Identical

Approach: The problem can be solved by traversing the circular linked list using the following idea:

This idea to solve this problem is similar to the problem "Check if given strings are rotations of each other or not". We'll convert given circular linked list into string and then check if second string is rotation of first string or not or vice versa.

Follow the steps below to implement the above idea:

Convert the first circular linked list into a string say S.
Convert the second circular linked list into a string say T.
Check lengths of S and T are not equal
- If true, then return false.
Store the concatenation of S with S itself in variable temp (i.e, temp = S+S).
Check if T is a substring in temp.
If true, then return true.
Otherwise, return false.

Below is the implementation of the above approach:

C++

// C++ program to Check that two circular
// linked list are identical or not

#include <bits/stdc++.h>
using namespace std;

// Circular Linked list Node Class
class Node {
public:
    int data;
    Node* next;

    // Constructor function
    Node(int data)
    {
        this->data = data;
        this->next = NULL;
    }
};

// Function to insert a node in
// tail in circular linked list
void insertNode(Node*& head, Node*& tail, int d)
{
    // First insertion in circular
    // linked list
    if (head == NULL) {
        Node* newNode = new Node(d);
        head = newNode;
        tail = newNode;
        newNode->next = newNode;
    }
    else {

        // Non-empty list
        Node* temp = new Node(d);
        temp->next = tail->next;
        tail->next = temp;
        tail = tail->next;
    }
}

// Function to print circular linked list
void print(Node* head)
{
    Node* curr = head;

    // If circular linked list is empty
    if (head == NULL) {
        cout << "List is Empty " << endl;
        return;
    }

    // Else iterate until node is NOT head
    do {
        cout << curr->data << " ";
        curr = curr->next;
    } while (curr != head);
    cout << endl;
}

string convertString(Node* head)
{
    Node* curr = head;
    string s = "";

    // If circular linked list is empty
    if (head == NULL) {
        return "";
    }

    // Else iterate until node is NOT head
    do {
        s += to_string(curr->data);
        s += "*";
        curr = curr->next;
    } while (curr != head);

    return s;
}

// Function to Check that two circular
// linked list are identical or not
bool checkIdentical(string& S, string& T)
{
    /* Check if sizes of two strings are same */
    if (S.length() != T.length())
        return false;

    string temp = S + S;
    return (temp.find(T) != string::npos);
}

// Driver Code
int main()
{

    Node* head1 = NULL;
    Node* tail1 = NULL;

    insertNode(head1, tail1, 1);
    insertNode(head1, tail1, 2);
    insertNode(head1, tail1, 3);
    insertNode(head1, tail1, 4);
    insertNode(head1, tail1, 5);
    insertNode(head1, tail1, 1);
    insertNode(head1, tail1, 2);
    insertNode(head1, tail1, 6);

    Node* head2 = NULL;
    Node* tail2 = NULL;

    insertNode(head2, tail2, 5);
    insertNode(head2, tail2, 1);
    insertNode(head2, tail2, 2);
    insertNode(head2, tail2, 6);
    insertNode(head2, tail2, 1);
    insertNode(head2, tail2, 2);
    insertNode(head2, tail2, 3);
    insertNode(head2, tail2, 4);

    cout << "First circular linked list: ";
    print(head1);

    cout << "Second circular linked list: ";
    print(head2);

    string S = convertString(head1);
    string T = convertString(head2);

    bool flag = checkIdentical(S, T);
    if (flag)
        cout << "Identical";
    else
        cout << "Not Identical";
    return 0;
}

Java

import java.util.*;

public class HelloWorld {

    static class Node {
        int data;
        Node next;

        Node(int d)
        {
            data = d;
            next = null;
        }
    }

    // Function to insert a node in
    // tail in circular linked list
    public static List<Node> insertNode(Node head,
                                        Node tail, int d)
    {
        // First insertion in circular
        // linked list
        if (head == null) {
            Node newNode = new Node(d);
            head = newNode;
            tail = newNode;
            newNode.next = newNode;
        }
        else {
            // Non-empty list
            Node temp = new Node(d);
            temp.next = tail.next;
            tail.next = temp;
            tail = tail.next;
        }

        List<Node> ans = new ArrayList<Node>();
        ans.add(head);
        ans.add(tail);

        return ans;
    }

    public static String convertString(Node head)
    {
        Node curr = head;
        String s = "";

        // If circular linked list is empty
        if (head == null) {
            return "";
        }

        // Else iterate until node is NOT head
        do {
            s += curr.data;
            s += "*";
            curr = curr.next;
        } while (curr != head);

        return s;
    }

    // Function to print circular linked list
    public static void print(Node head)
    {
        Node curr = head;

        // If circular linked list is empty
        if (head == null) {
            System.out.println("List is Empty");
            return;
        }

        // Else iterate until node is NOT head
        do {
            System.out.print(curr.data + " ");
            curr = curr.next;
        } while (curr != head);
        System.out.println();
    }

    // Function to Check that two circular
    // linked list are identical or not
    public static boolean checkIdentical(String S, String T)
    {
        /* Check if sizes of two strings are same */
        if (S.length() != T.length()) {
            return false;
        }

        String temp = S + S;

        if (temp.contains(T)) {
            return true;
        }
        return false;
    }

    public static void main(String[] args)
    {
        Node head1 = null;
        Node tail1 = null;
        List<Node> a = insertNode(head1, tail1, 1);
        head1 = a.get(0);
        tail1 = a.get(1);
        a = insertNode(head1, tail1, 2);
        head1 = a.get(0);
        tail1 = a.get(1);
        a = insertNode(head1, tail1, 3);
        head1 = a.get(0);
        tail1 = a.get(1);
        a = insertNode(head1, tail1, 4);
        head1 = a.get(0);
        tail1 = a.get(1);
        a = insertNode(head1, tail1, 5);
        head1 = a.get(0);
        tail1 = a.get(1);
        a = insertNode(head1, tail1, 1);
        head1 = a.get(0);
        tail1 = a.get(1);
        a = insertNode(head1, tail1, 2);
        head1 = a.get(0);
        tail1 = a.get(1);
        a = insertNode(head1, tail1, 6);
        head1 = a.get(0);
        tail1 = a.get(1);

        Node head2 = null;
        Node tail2 = null;

        a = insertNode(head2, tail2, 5);
        head2 = a.get(0);
        tail2 = a.get(1);
        a = insertNode(head2, tail2, 1);
        head2 = a.get(0);
        tail2 = a.get(1);
        a = insertNode(head2, tail2, 2);
        head2 = a.get(0);
        tail2 = a.get(1);
        a = insertNode(head2, tail2, 6);
        head2 = a.get(0);
        tail2 = a.get(1);
        a = insertNode(head2, tail2, 1);
        head2 = a.get(0);
        tail2 = a.get(1);
        a = insertNode(head2, tail2, 2);
        head2 = a.get(0);
        tail2 = a.get(1);
        a = insertNode(head2, tail2, 3);
        head2 = a.get(0);
        tail2 = a.get(1);
        a = insertNode(head2, tail2, 4);
        head2 = a.get(0);
        tail2 = a.get(1);

        System.out.print("First circular linked list: ");
        print(head1);

        System.out.print("Second circular linked list: ");
        print(head2);

        String S = convertString(head1);
        String T = convertString(head2);

        boolean flag = checkIdentical(S, T);
        if (flag)
            System.out.println("Identical");
        else
            System.out.println("Not Identical");
    }
}

Python3

# Python program to check that two circular
# linked list are identical or not

# Circular linked list node class
class Node:
    def __init__(self, data):
        self.data = data
        self.next = None

# function to insert a node in
# tail in circular linked list
def insertNode(head, tail, d):
    # first insertion in circular
    # linked list
    if(head is None):
        newNode = Node(d)
        head = newNode
        tail = newNode
        newNode.next = newNode
    else:
        # non-empty list
        temp = Node(d)
        temp.next = tail.next
        tail.next = temp
        tail = tail.next
    return head, tail


# function to print circular linked list
def printList(head):
    curr = head
    # if circular linked list is empty
    if(head is None):
        print("List is Empty.")
        return
    
    # else iterate until node is not head
    while True:
        print(curr.data, end=" ")
        curr = curr.next
        if(curr == head):
            break
    print("")


def convertString(head):
    curr = head
    s = ""
    
    # if circular linked list is empty
    if(head is None):
        return ""
    
    # else iterate until node is not head
    while True:
        s += str(curr.data)
        s += "*"
        curr = curr.next
        if(curr == head):
            break
    
    return s


# function to check that two circular
# linked list are identical or not
def checkIdentical(S, T):
    # check if sizes of two strings are same
    if(len(S) != len(T)):
        return False
    
    temp = S+S
    if T in temp:
        return True
    else:
        return False


# driver program
head1 = None
tail1 = None
head1, tail1 = insertNode(head1, tail1, 1)
head1, tail1 = insertNode(head1, tail1, 2)
head1, tail1 = insertNode(head1, tail1, 3)
head1, tail1 = insertNode(head1, tail1, 4)
head1, tail1 = insertNode(head1, tail1, 5)
head1, tail1 = insertNode(head1, tail1, 1)
head1, tail1 = insertNode(head1, tail1, 2)
head1, tail1 = insertNode(head1, tail1, 6)

head2 = None
tail2 = None
head2, tail2 = insertNode(head2, tail2, 5)
head2, tail2 = insertNode(head2, tail2, 1)
head2, tail2 = insertNode(head2, tail2, 2)
head2, tail2 = insertNode(head2, tail2, 6)
head2, tail2 = insertNode(head2, tail2, 1)
head2, tail2 = insertNode(head2, tail2, 2)
head2, tail2 = insertNode(head2, tail2, 3)
head2, tail2 = insertNode(head2, tail2, 4)

print("First circular linked list : ")
printList(head1)

print("Second Circular linked list : ")
printList(head2)

S = convertString(head1)
T = convertString(head2)

flag = checkIdentical(S, T)
if(flag):
    print("Identical")
else:
    print("Not Identical")
# This code is contributed by Kirti Agarwal(kirtiagarwal23121999)

JavaScript

// JavaScript program to check thattwo circular
// linked list are identical or not

// Circular linked list nodeclass
class Node{
    constructor(data){
        this.data = data;
        this.next = null;
    }
}

// functio to insert a node in
// tail in circular linked list
function insertNode(head, tail, d){
    // first insertion in circular
    // linked list
    if(head == null){
        let newNode = new Node(d);
        head = newNode;
        tail = newNode;
        newNode.next = newNode;
    }
    else{
        // non-empty list
        let temp = new Node(d);
        temp.next = tail.next;
        tail.next = temp;
        tail = tail.next;
    }
    return [head, tail];
}

// functio to print circular linked list
function print(head){
    let curr = head;
    
    // if circular linked list is empty
    if(head == null){
        console.log("List is Empty.");
        return;
    }
    
    // else iterate until node is not head
    do{
        console.log(curr.data + " ");
        curr = curr.next;
    }while(curr != head);
    console.log("");
}

function convertString(head){
    let curr = head;
    let s = "";
    
    // if circular linked list is empty
    if(head == null) return "";
    
    // else iterate until node is not head
    do{
        s += (curr.data).toString();
        s += "*";
        curr = curr.next;
    }while(curr != head);
    
    return s;
}

// function to check that two circular
// linked list are identical or not
function checkIdentical(S, T){
    // check if sizes of two strings are same
    if(S.length != T.length) return false;
    
    let temp = S+S;
    if(temp.includes(T)) return true;
    else return false;
}

// driver program
let head1 = null;
let tail1 = null;
[head1, tail1] = insertNode(head1, tail1, 1);
[head1, tail1] = insertNode(head1, tail1, 2);
[head1, tail1] = insertNode(head1, tail1, 3);
[head1, tail1] = insertNode(head1, tail1, 4);
[head1, tail1] = insertNode(head1, tail1, 5);
[head1, tail1] = insertNode(head1, tail1, 1);
[head1, tail1] = insertNode(head1, tail1, 2);
[head1, tail1] = insertNode(head1, tail1, 6);

let head2 = null;
let tail2 = null;
[head2, tail2] = insertNode(head2, tail2, 5);
[head2, tail2] = insertNode(head2, tail2, 1);
[head2, tail2] = insertNode(head2, tail2, 2);
[head2, tail2] = insertNode(head2, tail2, 6);
[head2, tail2] = insertNode(head2, tail2, 1);
[head2, tail2] = insertNode(head2, tail2, 2);
[head2, tail2] = insertNode(head2, tail2, 3);
[head2, tail2] = insertNode(head2, tail2, 4);

console.log("First circular linked list : ");
print(head1);

console.log("Second circular linked list : ");
print(head2);

let S = convertString(head1);
let T = convertString(head2);

let flag = checkIdentical(S, T);
if(flag) console.log("Identical");
else console.log("Not Identical");

// THIS CODE IS CONTRIBUTED BY YASH AGARWAL(YASHAGARWAL2852002)

using System;
using System.Collections;
using System.Collections.Generic;
using System.Linq;

// C# program to Check that two circular
// linked list are identical or not

class HelloWorld {
    
    public class Node
    {
        public int data;
        public Node next;
        public Node(int d) {data = d; next = null;}
    }

    // Function to insert a node in
    // tail in circular linked list
    public static List<Node>  insertNode(Node head, Node tail, int d)
    {
        // First insertion in circular
        // linked list
        if (head == null) {
            Node newNode = new Node(d);
            head = newNode;
            tail = newNode;
            newNode.next = newNode;
        }
        else {

            // Non-empty list
            Node temp = new Node(d);
            temp.next = tail.next;
            tail.next = temp;
            tail = tail.next;
        }
        
        List<Node> ans = new List<Node>();
        ans.Add(head);
        ans.Add(tail);
        
        return ans;
    }

    public static string convertString(Node head)
    {
        Node curr = head;
        string s = "";

        // If circular linked list is empty
        if (head == null) {
            return "";
        }

        // Else iterate until node is NOT head
        do {
            s += curr.data.ToString();
            s += "*";
            curr = curr.next;
        } while (curr != head);

        return s;
    }

    
    // Function to print circular linked list
    public static void print(Node head)
    {
        Node curr = head;

        // If circular linked list is empty
        if (head == null) {
            
            Console.WriteLine("List is Empty ");
            return;
        }

        // Else iterate until node is NOT head
        do {
            Console.Write(curr.data + " ");
            curr = curr.next;
        } while (curr != head);
        Console.WriteLine();
    }
    
    // Function to Check that two circular
    // linked list are identical or not
    public static bool checkIdentical(string S, string T)
    {
        /* Check if sizes of two strings are same */
        if (S.Length != T.Length)
            return false;

        string temp = S + S;
        
        if(temp.Contains(T)) return true;
        return false;
    }
    
    static void Main() {

        Node head1 = null;
        Node tail1 = null;

        List<Node> a = insertNode(head1, tail1, 1);
        head1 = a[0];
        tail1 = a[1];
        
        a = insertNode(head1, tail1, 2);
        head1 = a[0];
        tail1 = a[1];
        
        a = insertNode(head1, tail1, 3);
        head1 = a[0];
        tail1 = a[1];
        
        a = insertNode(head1, tail1, 4);
        head1 = a[0];
        tail1 = a[1];
        
        a = insertNode(head1, tail1, 5);
        head1 = a[0];
        tail1 = a[1];
        
        a = insertNode(head1, tail1, 1);
        head1 = a[0];
        tail1 = a[1];
        
        a = insertNode(head1, tail1, 2);
        head1 = a[0];
        tail1 = a[1];
        
        a = insertNode(head1, tail1, 6);
        head1 = a[0];
        tail1 = a[1];


        Node head2 = null;
        Node tail2 = null;

        a = insertNode(head2, tail2, 5);
        head2 = a[0];
        tail2 = a[1];
        
        a = insertNode(head2, tail2, 1);
        head2 = a[0];
        tail2 = a[1];
        
        a = insertNode(head2, tail2, 2);
        head2 = a[0];
        tail2 = a[1];
        
        a = insertNode(head2, tail2, 6);
        head2 = a[0];
        tail2 = a[1];
        
        a = insertNode(head2, tail2, 1);
        head2 = a[0];
        tail2 = a[1];
        
        a = insertNode(head2, tail2, 2);
        head2 = a[0];
        tail2 = a[1];
        
        a = insertNode(head2, tail2, 3);
        head2 = a[0];
        tail2 = a[1];
        
        a = insertNode(head2, tail2, 4);
        head2 = a[0];
        tail2 = a[1];

        Console.Write("First circular linked list: ");
        print(head1);

        Console.Write("Second circular linked list: ");
        print(head2);

        string S = convertString(head1);
        string T = convertString(head2);

        bool flag = checkIdentical(S, T);
        if (flag)
            Console.WriteLine("Identical");
        else
            Console.WriteLine("Not Identical");
    }
}

// The code is contributed by Nidhi goel.

Output

First circular linked list: 1 2 3 4 5 1 2 6 
Second circular linked list: 5 1 2 6 1 2 3 4 
Identical

Time Complexity: O(N)
Auxiliary Space: O(1)

Javascript Program To Check If Two Linked Lists Are Identical

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