Memory efficient doubly linked list
Last Updated : 29 Aug, 2024
We need to implement a doubly linked list with the use of a single pointer in each node. For that we are given a stream of data of size n for the linked list, your task is to make the function insert() and getList(). The insert() function pushes (or inserts at the beginning) the given data in the linked list and the getList() function returns the linked list as a list.
Note: The List should be printed in both forward and backward direction.
Examples
Input: head= 40<->30<->20<->10
Output: 40 30 20 10
10 20 30 40
Input: head= 5<->4<->3<->2<->1
Output: 5 4 3 2 1
1 2 3 4 5
[Expected Approach] Using Bitwise XOR - O(n) Time and O(1) Space
We know that each node in a doubly-linked list has two pointer fields which contain the addresses of the previous and next node. On the other hand, each node of the XOR linked list requires only a single pointer field, which doesn’t store the actual memory addresses but stores the bitwise XOR of addresses for its previous and next node.
Below is the implementation of the above approach :
C++ // C++ program Implements a doubly linked // list using XOR pointers. #include <bits/stdc++.h> using namespace std; class Node { public: int data; Node* npx; Node(int x) { data = x; npx = nullptr; } }; // XOR function to get XOR of two pointers Node* XOR(Node* a, Node* b) { return reinterpret_cast<Node*>(reinterpret_cast<uintptr_t>(a) ^ reinterpret_cast<uintptr_t>(b)); } // Function to insert a node at the front of the list Node* insert(Node* head, int data) { // Create a new node with the given data Node* new_node = new Node(data); // Make the new node's npx point to the head new_node->npx = XOR(head, nullptr); // Update npx of the head if it's not NULL if (head != nullptr) { Node* next = XOR(head->npx, nullptr); head->npx = XOR(new_node, next); } // Return the new node as the new head return new_node; } // Function to retrieve the list as a vector vector<int> getList(Node* head) { vector<int> vec; Node* curr = head; Node* prev = nullptr; Node* next; while (curr != nullptr) { // Add current node's data to vector vec.push_back(curr->data); // Calculate the next node using XOR next = XOR(prev, curr->npx); // Update previous and current nodes prev = curr; curr = next; } return vec; } int main() { // Create a hard-coded linked list: // 40 <-> 30 <-> 20 <-> 10 (since we insert at the // front) Node* head = nullptr; head = insert(head, 10); head = insert(head, 20); head = insert(head, 30); head = insert(head, 40); vector<int> list = getList(head); for(int i = 0; i < list.size(); ++i) { cout<< list[i] <<" "; } cout << endl; for(int i = list.size() - 1; i >= 0; --i) { cout<< list[i] <<" "; } cout << endl; return 0; } // C program Implements a doubly linked // list using XOR pointers #include <stdio.h> #include <stdlib.h> #include <stdint.h> struct Node { int data; struct Node* npx; }; struct Node* createNode(int data); // XOR function to get XOR of two pointers struct Node* XOR(struct Node* a, struct Node* b) { return (struct Node*)((uintptr_t)(a) ^ (uintptr_t)(b)); } // Function to insert a node at the front of the list struct Node* insert(struct Node* head, int data) { // Create a new node with the given data struct Node* new_node = createNode(data); // Make the new node's npx point to the head new_node->npx = XOR(head, NULL); // Update npx of the head if it's not NULL if (head != NULL) { struct Node* next = XOR(head->npx, NULL); head->npx = XOR(new_node, next); } // Return the new node as the new head return new_node; } // Function to retrieve the list as an array void getList(struct Node* head, int* arr, int* len) { struct Node* curr = head; struct Node* prev = NULL; struct Node* next; // Initialize array index *len = 0; while (curr != NULL) { // Add current node's data to array arr[(*len)++] = curr->data; // Calculate the next node using XOR next = XOR(prev, curr->npx); // Update previous and current nodes prev = curr; curr = next; } } struct Node* createNode(int data) { struct Node* new_node = (struct Node*)malloc(sizeof(struct Node)); new_node->data = data; new_node->npx = NULL; return new_node; } int main() { // Create a hard-coded linked list: // 40 <-> 30 <-> 20 <-> 10 (since we insert at the // front) struct Node* head = NULL; int list[100]; int len, i; head = insert(head, 10); head = insert(head, 20); head = insert(head, 30); head = insert(head, 40); getList(head, list, &len); for (i = 0; i < len; ++i) { printf("%d ", list[i]); } printf("\n"); for (i = len - 1; i >= 0; --i) { printf("%d ", list[i]); } printf("\n"); return 0; } // Java program Implements a doubly linked // list using XOR pointers import java.util.ArrayList; class Node { int data; Node prev; Node next; Node(int x) { this.data = x; this.prev = null; this.next = null; } } public class GfG { // Function to insert a node at the front static Node insert(Node head, int data) { // Create a new node with the given data Node newNode = new Node(data); // Update head's previous pointer if the list is not // empty if (head != null) { head.prev = newNode; newNode.next = head; } // Return the new node as the new head return newNode; } // Function to retrieve the list as an ArrayList static ArrayList<Integer> getList(Node head) { ArrayList<Integer> list = new ArrayList<>(); // Start from the head and traverse the list Node current = head; while (current != null) { list.add(current.data); current = current.next; } return list; } public static void main(String[] args) { // Create a hard-coded linked list: // 40 <-> 30 <-> 20 <-> 10 (since we insert at the // front) Node head = null; head = insert(head, 10); head = insert(head, 20); head = insert(head, 30); head = insert(head, 40); ArrayList<Integer> list = getList(head); for (int i = 0; i < list.size(); i++) { System.out.print(list.get(i) + " "); } System.out.println(); for (int i = list.size() - 1; i >= 0; i--) { System.out.print(list.get(i) + " "); } System.out.println(); } } # Python program Implements a doubly linked # list using XOR pointers class Node: def __init__(self, data): self.data = data self.prev = None self.next = None # Function to insert a node at the front def insert(head, data): # Create a new node with the given data new_node = Node(data) # Update head's previous pointer if list is not empty if head is not None: head.prev = new_node new_node.next = head # Return the new node as the new head return new_node # Function to retrieve the list as a list def getList(head): result = [] # Start from the head and traverse the list current = head while current is not None: result.append(current.data) current = current.next return result if __name__ == "__main__": # Create a hard-coded linked list: # 40 <-> 30 <-> 20 <-> 10 (since we insert at the # front) head = None head = insert(head, 10) head = insert(head, 20) head = insert(head, 30) head = insert(head, 40) result_list = getList(head) for i in range(len(result_list)): print(result_list[i], end=" ") print() for i in range(len(result_list) - 1, -1, -1): print(result_list[i], end=" ") print()
// C# program Implements a doubly linked // list using XOR pointers using System; using System.Collections.Generic; class Node { public int data; public Node prev; public Node next; public Node(int x) { data = x; prev = null; next = null; } } class GfG { // Function to insert a node at the front static Node Insert(Node head, int data) { // Create a new node with the given data Node newNode = new Node(data); // Update head's previous pointer if // the list is not empty if (head != null) { head.prev = newNode; newNode.next = head; } // Return the new node as the new head return newNode; } // Function to retrieve the list as a List<int> static List<int> GetList(Node head) { List<int> result = new List<int>(); // Start from the head and traverse the list Node current = head; while (current != null) { result.Add(current.data); current = current.next; } return result; } public static void Main(string[] args) { // Create a hard-coded linked list: // 40 <-> 30 <-> 20 <-> 10 //(since we insert at the front) Node head = null; head = Insert(head, 10); head = Insert(head, 20); head = Insert(head, 30); head = Insert(head, 40); List<int> resultList = GetList(head); foreach (int num in resultList) { Console.Write(num + " "); } Console.WriteLine(); for (int i = resultList.Count - 1; i >= 0; i--) { Console.Write(resultList[i] + " "); } Console.WriteLine(); } } // Javascript program Implements a doubly linked // list using XOR pointers class Node { constructor(data) { // Initialize node data and pointers this.data = data; this.prev = null; this.next = null; } } // Function to insert a node at the front function insert(head, data) { // Create a new node with the given data const newNode = new Node(data); // Update head's previous pointer if list is not empty if (head !== null) { head.prev = newNode; newNode.next = head; } // Return the new node as the new head return newNode; } // Function to retrieve the list as an array function getList(head) { const result = []; // Start from the head and traverse the list let current = head; while (current !== null) { result.push(current.data); current = current.next; } return result; } // Create a hard-coded linked list: // 40 <-> 30 <-> 20 <-> 10 (since we insert at the // front) let head = null; head = insert(head, 10); head = insert(head, 20); head = insert(head, 30); head = insert(head, 40); const resultList = getList(head); for (let i = 0; i < resultList.length; i++) { console.log(resultList[i] + " "); } for (let i = resultList.length - 1; i >= 0; i--) { console.log(resultList[i] + " "); } Output40 30 20 10 10 20 30 40
Time Complexity: O(n) for both insertion and retrieval, where n is the number of nodes.
Auxiliary Space: O(1) for insertion, O(n) for storing the list in an array
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