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Check if elements of Linked List are present in pair

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  • Difficulty Level : Easy
  • Last Updated : 23 Nov, 2022
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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:  

  • Initialize 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++




// 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;
}

Java




// 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

Python3




# Python3 program to check if elements of
# linked lists are present in pair
 
# A linked list node
class Node:
    def __init__(self):
        self.data = 0
        self.next = None
 
# Function to check if elements of
# linked list are present in pair
def isPair( head):
    xxor = 0
    temp = head
 
    while (temp != None) :
        xxor = xxor ^ temp.data
        temp = temp.next
 
    return xxor
 
# Function to add a node at the
# beginning of Linked List
def push( head_ref, new_data):
 
    # allocate node
    new_node = 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
     
    return head_ref
 
# Driver code
 
first = None
 
# First constructed linked list is:
# 10 . 34 . 1 . 10 . 34 . 1
first = push(first, 1)
first = push(first, 34)
first = push(first, 10)
first = push(first, 1)
first = push(first, 34)
first = push(first, 10)
 
# Calling function to check pair elements
if (not isPair(first)):
    print( "Yes" )
     
else :
    print( "No" )
     
# This code is contributed by Arnab Kundu

C#




// 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

Javascript




<script>
 
      // JavaScript program to check if elements of
      // linked lists are present in pair
      // Node Class
      class Node {
        // Constructor to create a new node
        constructor(d) {
          this.data = d;
          this.next = null;
        }
      }
 
      // function to insert a node at the beginning
      // of the Singly Linked List
      function push(head, data) {
        var newNode = new Node(data);
        newNode.next = head;
        head = newNode;
        return head;
      }
 
      // Function to check if elements of
      // linked list are present in pair
      function isPair(head) {
        var xxor = 0;
        var temp = head;
        while (temp != null) {
          xxor ^= temp.data;
          temp = temp.next;
        }
        return xxor != 0;
      }
 
      // Driver code
      var 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)) {
        document.write("Yes");
      } else {
        document.write("No");
      }
       
</script>

Output

Yes

Time Complexity: O(n), where n is the number of nodes in the linked list
Auxiliary Space: O(1)


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