Check if elements of Linked List are present in pair

Given a singly linked list of integers. The task is to check if each element in the linked list is present in a pair i.e. all elements occur even no. of times.

Examples:

Input: 1 -> 2 -> 3 -> 3 -> 1 -> 2
Output: Yes

Input: 10 -> 20 -> 30 -> 20
Output: No

Approach:



  • Initialise a temp node pointing to head.
  • Take a variable to calculate XOR of all elements.
  • Start traversing linked list and keep calculating the XOR with node->data.
  • Return true if XOR is 0, else return false.

Below is the implementation of above approach:

C++

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// C++ program to check if elements of
// linked lists are present in pair
#include <bits/stdc++.h>
  
using namespace std;
  
// A linked list node
struct Node {
    int data;
    struct Node* next;
};
  
// Function to check if elements of
// linked list are present in pair
bool isPair(struct Node* head)
{
  
    int xxor = 0;
  
    struct Node* temp = head;
  
    while (temp != NULL) {
        xxor ^= temp->data;
        temp = temp->next;
    }
  
    return xxor;
}
  
// Function to add a node at the
// beginning of Linked List
void push(struct Node** head_ref, int new_data)
{
    /* allocate node */
    struct Node* new_node = (struct Node*)malloc(sizeof(struct Node));
  
    /* put in the data */
    new_node->data = new_data;
  
    /* link the old list off the new node */
    new_node->next = (*head_ref);
  
    /* move the head to point to the new node */
    (*head_ref) = new_node;
}
  
// Driver program to test above function
int main()
{
    struct Node* first = NULL;
  
    /* First constructed linked list is: 
    10 -> 34 -> 1 -> 10 -> 34 -> 1 */
    push(&first, 1);
    push(&first, 34);
    push(&first, 10);
    push(&first, 1);
    push(&first, 34);
    push(&first, 10);
  
    // Calling function to check pair elements
    if (!isPair(first)) {
        cout << "Yes" << endl;
    }
    else {
        cout << "No" << endl;
    }
  
    return 0;
}

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Java

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// Java program to check if elements of 
// linked lists are present in pair 
  
// Node Class 
class Node
{
    int data;
    Node next;
  
    // Constructor to create a new node
    Node(int d)
    {
        data = d;
        next = null;
    }
}
  
class SLL 
{
  
    // function to insert a node at the beginning
    // of the Singly Linked List
    static Node push(Node head, int data) 
    {
        Node newNode = new Node(data);
        newNode.next = head;
        head = newNode;
        return head;
    }
  
    // Function to check if elements of
    // linked list are present in pair
    static boolean isPair(Node head)
    {
        int xxor = 0;
        Node temp = head;
        while (temp != null)
        {
            xxor ^= temp.data;
            temp = temp.next;
        }
        return xxor != 0;
    }
  
    // Driver code
    public static void main(String[] args) 
    {
        Node head = null;
  
        // First constructed linked list
        // 10 -> 34 -> 1 -> 10 -> 34 -> 1
  
        head = push(head, 1);
        head = push(head, 34);
        head = push(head, 10);
        head = push(head, 1);
        head = push(head, 34);
        head = push(head, 10);
  
        // Calling function to check pair elements
        if (!isPair(head))
        {
            System.out.println("Yes");
        
        else
        {
            System.out.println("No");
        }
    }
}
  
// This code is contributed by Vivekkumar Singh

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C#

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// C# program to check if elements of 
// linked lists are present in pair 
using System;
  
// Node Class 
public class Node
{
    public int data;
    public Node next;
  
    // Constructor to create a new node
    public Node(int d)
    {
        data = d;
        next = null;
    }
}
  
public class SLL 
{
  
    // function to insert a node at the beginning
    // of the Singly Linked List
    static Node push(Node head, int data) 
    {
        Node newNode = new Node(data);
        newNode.next = head;
        head = newNode;
        return head;
    }
  
    // Function to check if elements of
    // linked list are present in pair
    static Boolean isPair(Node head)
    {
        int xxor = 0;
        Node temp = head;
        while (temp != null)
        {
            xxor ^= temp.data;
            temp = temp.next;
        }
        return xxor != 0;
    }
  
    // Driver code
    public static void Main(String[] args) 
    {
        Node head = null;
  
        // First constructed linked list
        // 10 -> 34 -> 1 -> 10 -> 34 -> 1
  
        head = push(head, 1);
        head = push(head, 34);
        head = push(head, 10);
        head = push(head, 1);
        head = push(head, 34);
        head = push(head, 10);
  
        // Calling function to check pair elements
        if (!isPair(head))
        {
            Console.WriteLine("Yes");
        
        else
        {
            Console.WriteLine("No");
        }
    }
}
  
// This code is contributed by Rajput-Ji

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Output:

Yes


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