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HomeData ModellingData Structure & AlgorithmXOR Linked List – Find the middle node

XOR Linked List – Find the middle node

Given an XOR linked list, the task is to find the middle node of the given XOR linked list.

Examples:

Input: 4 –> 7 –> 5 
Output:
Explanation: 
The middle node of the given XOR list is 7.

Input: 4 –> 7 –> 5 –> 1 
Output: 7 5 
Explanation: 
The two middle nodes of the XOR linked list with even number of nodes are 7 and 5. 
 

Approach: Follow the steps below to solve the problem:

  • Traverse to (Length / 2)th node of the Linked List.
  • If the number of nodes is found to be odd, then print (Length + 1) / 2 th node as the only middle node.
  • If the number of nodes is found to be even, then print both Length / 2 th node and (Length / 2) + 1 th node as the middle nodes.

Below is the implementation of the above approach:

C++




// C++ program to implement
// the above approach
 
#include <bits/stdc++.h>
#include <inttypes.h>
using namespace std;
 
// Structure of a node
// in XOR linked list
struct Node {
 
    // Stores data value
    // of a node
    int data;
 
    // Stores XOR of previous
    // pointer and next pointer
    struct Node* nxp;
};
 
// Function to find the XOR of two nodes
struct Node* XOR(struct Node* a, struct Node* b)
{
    return (struct Node*)((uintptr_t)(a) ^ (uintptr_t)(b));
}
 
// Function to insert a node with
// given value at given position
struct Node* insert(struct Node** head, int value)
{
 
    // If XOR linked list is empty
    if (*head == NULL) {
 
        // Initialize a new Node
        struct Node* node = new Node;
 
        // Stores data value in
        // the node
        node->data = value;
 
        // Stores XOR of previous
        // and next pointer
        node->nxp = XOR(NULL, NULL);
 
        // Update pointer of head node
        *head = node;
    }
 
    // If the XOR linked list
    // is not empty
    else {
 
        // Stores the address
        // of current node
        struct Node* curr = *head;
 
        // Stores the address
        // of previous node
        struct Node* prev = NULL;
 
        // Initialize a new Node
        struct Node* node
            = new Node();
 
        // Update curr node address
        curr->nxp = XOR(node, XOR(NULL, curr->nxp));
 
        // Update new node address
        node->nxp = XOR(NULL, curr);
 
        // Update head
        *head = node;
 
        // Update data value of
        // current node
        node->data = value;
    }
    return *head;
}
 
// Function to print the middle node
int printMiddle(struct Node** head, int len)
{
    int count = 0;
 
    // Stores XOR pointer
    // in current node
    struct Node* curr = *head;
 
    // Stores XOR pointer of
    // in previous Node
    struct Node* prev = NULL;
 
    // Stores XOR pointer of
    // in next node
    struct Node* next;
 
    int middle = (int)len / 2;
 
    // Traverse XOR linked list
    while (count != middle) {
 
        // Forward traversal
        next = XOR(prev, curr->nxp);
 
        // Update prev
        prev = curr;
 
        // Update curr
        curr = next;
 
        count++;
    }
 
    // If the length of the
    // linked list is odd
    if (len & 1) {
        cout << curr->data << " ";
    }
 
    // If the length of the
    // linked list is even
    else {
        cout << prev->data << " " << curr->data << " ";
    }
}
 
// Driver Code
int main()
{
    /* Create following XOR Linked List
    head --> 4 –> 7 –> 5 */
    struct Node* head = NULL;
    insert(&head, 4);
    insert(&head, 7);
    insert(&head, 5);
 
    printMiddle(&head, 3);
 
    return (0);
}


C




// C program to implement
// the above approach
 
#include <inttypes.h>
#include <stdio.h>
#include <stdlib.h>
 
// Structure of a node
// in XOR linked list
struct Node {
 
    // Stores data value
    // of a node
    int data;
 
    // Stores XOR of previous
    // pointer and next pointer
    struct Node* nxp;
};
 
// Function to find the XOR of two nodes
struct Node* XOR(struct Node* a,
                 struct Node* b)
{
    return (struct Node*)((uintptr_t)(a)
                          ^ (uintptr_t)(b));
}
 
// Function to insert a node with
// given value at given position
struct Node* insert(struct Node** head,
                    int value)
{
 
    // If XOR linked list is empty
    if (*head == NULL) {
 
        // Initialize a new Node
        struct Node* node
            = (struct Node*)malloc(
                sizeof(struct Node));
 
        // Stores data value in
        // the node
        node->data = value;
 
        // Stores XOR of previous
        // and next pointer
        node->nxp = XOR(NULL, NULL);
 
        // Update pointer of head node
        *head = node;
    }
 
    // If the XOR linked list
    // is not empty
    else {
 
        // Stores the address
        // of current node
        struct Node* curr = *head;
 
        // Stores the address
        // of previous node
        struct Node* prev = NULL;
 
        // Initialize a new Node
        struct Node* node
            = (struct Node*)malloc(
                sizeof(struct Node));
 
        // Update curr node address
        curr->nxp = XOR(
            node, XOR(NULL, curr->nxp));
 
        // Update new node address
        node->nxp = XOR(NULL, curr);
 
        // Update head
        *head = node;
 
        // Update data value of
        // current node
        node->data = value;
    }
    return *head;
}
 
// Function to print the middle node
int printMiddle(struct Node** head, int len)
{
    int count = 0;
 
    // Stores XOR pointer
    // in current node
    struct Node* curr = *head;
 
    // Stores XOR pointer of
    // in previous Node
    struct Node* prev = NULL;
 
    // Stores XOR pointer of
    // in next node
    struct Node* next;
 
    int middle = (int)len / 2;
 
    // Traverse XOR linked list
    while (count != middle) {
 
        // Forward traversal
        next = XOR(prev, curr->nxp);
 
        // Update prev
        prev = curr;
 
        // Update curr
        curr = next;
 
        count++;
    }
 
    // If the length of the
    // linked list is odd
    if (len & 1) {
        printf("%d", curr->data);
    }
 
    // If the length of the
    // linked list is even
    else {
        printf("%d %d", prev->data,
               curr->data);
    }
}
 
// Driver Code
int main()
{
    /* Create following XOR Linked List
    head --> 4 –> 7 –> 5 */
    struct Node* head = NULL;
    insert(&head, 4);
    insert(&head, 7);
    insert(&head, 5);
 
    printMiddle(&head, 3);
 
    return (0);
 
}


Python3




# C program to implement
# the above approach
import ctypes
 
 
# Structure of a node in XOR linked list
class Node:
     
    def __init__(self, value):
        self.value = value
        self.npx = 0
 
 
# create linked list class
class XorLinkedList:
  
    # constructor
    def __init__(self):
        self.head = None
        self.tail = None
        self.__nodes = []
         
     
    # Function to insert a node with given value at given position
    def insert(self, value):
         
        # Initialize a new Node
        node = Node(value)
         
        # Check If XOR linked list is empty
        if self.head is None:
             
            # Update pointer of head node
            self.head = node
             
            # Update pointer of tail node
            self.tail = node
             
        else:
             
            # Update curr node address
            self.head.npx = id(node) ^ self.head.npx
             
            # Update new node address
            node.npx = id(self.head)
             
            # Update head
            self.head = node
             
        # push node
        self.__nodes.append(node)
         
         
    # method to get length of linked list
    def Length(self):
        if not self.isEmpty():
            prev_id = 0
            node = self.head
            next_id = 1
            count = 1
            while next_id:
                next_id = prev_id ^ node.npx
                if next_id:
                    prev_id = id(node)
                    node = self.__type_cast(next_id)
                    count += 1
                else:
                    return count
        else:
            return 0
         
    # Function to print elements of the XOR Linked List
    def printMiddle(self, length):
  
        if self.head != None:
            prev_id = 0
            node = self.head
            next_id = 1
             
            # Traverse XOR linked list
            middle = length // 2
            count = 0
            prev = None
             
            while count != middle:
                 
                count = count + 1
                 
                # Forward traversal
                next_id = prev_id ^ node.npx
                 
                if next_id:
                     
                    # Update prev
                    prev_id = id(node)
                     
                    # Update curr
                    prev = node
                    node = self.__type_cast(next_id)
 
                else:
                    return
                 
            if length % 2 != 0:
                print(node.value, end = ' ')
            else:
                print(prev.value, node.value, end = ' ')
 
                 
    # method to check if the linked list is empty or not
    def isEmpty(self):
        if self.head is None:
            return True
        return False
     
    # method to return a new instance of type
    def __type_cast(self, id):
        return ctypes.cast(id, ctypes.py_object).value
     
 
# Create following XOR Linked List
# head-->40<-->30<-->20<-->10
head = XorLinkedList()
head.insert(4)
head.insert(7)
head.insert(5)
 
 
# Reverse the XOR Linked List to give
# head-->10<-->20<-->30<-->40
length = head.Length()
head.printMiddle(length)
 
 
# This code is contributed by Nidhi goel.


Javascript




// JavaScript program to implement the above approach
class Node {
  constructor(value) {
    this.value = value;
    this.npx = 0;
  }
}
 
// create linked list class
class XorLinkedList {
  // constructor
  constructor() {
    this.head = null;
    this.tail = null;
    this.__nodes = [];
  }
 
  // Function to insert a node with given value at given position
  insert(value) {
    // Initialize a new Node
    const node = new Node(value);
 
    // Check If XOR linked list is empty
    if (this.head === null) {
      // Update pointer of head node
      this.head = node;
      // Update pointer of tail node
      this.tail = node;
    } else {
      // Update curr node address
      this.head.npx = this.__getId(node) ^ this.head.npx;
      // Update new node address
      node.npx = this.__getId(this.head);
      // Update head
      this.head = node;
    }
    // push node
    this.__nodes.push(node);
  }
 
  // method to get length of linked list
  length() {
    if (!this.isEmpty()) {
      let prevId = 0;
      let node = this.head;
      let nextId = 1;
      let count = 1;
      while (nextId) {
        nextId = prevId ^ node.npx;
        if (nextId) {
          prevId = this.__getId(node);
          node = this.__typeCast(nextId);
          count += 1;
        } else {
          return count;
        }
      }
    } else {
      return 0;
    }
  }
 
  // Function to print elements of the XOR Linked List
  printMiddle(length) {
    if (this.head !== null) {
      let prevId = 0;
      let node = this.head;
      let nextId = 1;
      // Traverse XOR linked list
      const middle = Math.floor(length / 2);
      let count = 0;
      let prev = null;
      while (count !== middle) {
        count = count + 1;
        // Forward traversal
        nextId = prevId ^ node.npx;
        if (nextId) {
          // Update prev
          prevId = this.__getId(node);
          // Update curr
          prev = node;
          node = this.__typeCast(nextId);
        } else {
          return;
        }
      }
      if (length % 2 !== 0) {
        console.log(node.value);
      } else {
        console.log(prev.value, node.value);
      }
    }
  }
 
  // method to check if the linked list is empty or not
  isEmpty() {
    if (this.head === null) {
      return true;
    }
    return false;
  }
 
  // method to return a new instance of type
  __typeCast(id) {
    return ctypes.cast(id, ctypes.py_object).value;
  }
 
  // method to get the unique ID of an object
  __getId(obj) {
    return obj && obj.__unique_id__;
  }
}
 
// Create following XOR Linked List
// head-->40<-->30<-->20<-->10
const head = new XorLinkedList();
head.insert(4);
head.insert(5);
head.insert(7);
 
 
// Reverse the XOR Linked List to give
// head-->10<-->20<-->30<-->40
const length = head.length();
head.printMiddle(length);
 
//this is generated by chetanbargal


Output: 

7

 

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

 

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