Given two Linked List, the task is to create a Linked List to store the difference of Linked List 1 with Linked List 2, i.e. the elements present in List 1 but not in List 2.
Examples:
Input:
List1: 10 -> 15 -> 4 ->20,
List2: 8 -> 4 -> 2 -> 10
Output: 15 -> 20
Explanation:
In the given linked list elements 15 and 20 are present in the list 1 but not in list 2.
Input:
List1: 2 -> 4 -> 8 -> 10,
List2: 8 -> 10
Output: 2 -> 4
Explanation:
In the given linked list 1 elements 2 and 4 are present in the list 1 but not in list 2.
Approach:
- Sort both Linked Lists using merge sort.
- Linearly scan both sorted lists to get the difference with two pointers on it p1 and p2 and compare the data of the nodes in the linked list and perform following in below three cases –
- If p1.data == p2.data then, p1.data cannot be in the difference list, So move the pointers p1 and p2 ahead.
- If p1.data > p2.data then, p1.data may be present in list 2 in further nodes, So move the pointer p2 ahead.
- If p1.data > p2.data then, p1.data cannot be present in list 2 now, So add the data of p1 into difference list and move pointer p1 ahead.
- If the end of list 2 is reached, insert all the remaining elements of list 1 into the difference list.
Below is the implementation of the above approach.
C++
//C++ program to implement above approach#include <iostream>class Node {public: int data; Node* next; Node(int val) : data(val), next(nullptr) {}};class LinkedList {public: Node* head; LinkedList() : head(nullptr) {} // Function to insert a node at the end of the linked list void append(int data) { Node* temp = new Node(data); if (head == nullptr) { head = temp; } else { Node* p = head; while (p->next != nullptr) { p = p->next; } p->next = temp; } } // Function to find the middle node of the linked list Node* get_mid(Node* head) { if (head == nullptr) { return head; } Node* slow = head; Node* fast = head; while (fast->next != nullptr && fast->next->next != nullptr) { slow = slow->next; fast = fast->next->next; } return slow; } // Recursive method to merge two halves after sorting Node* merge(Node* l, Node* r) { if (l == nullptr) return r; if (r == nullptr) return l; Node* result; if (l->data <= r->data) { result = l; result->next = merge(l->next, r); } else { result = r; result->next = merge(l, r->next); } return result; } // Recursive method to divide the list into two halves until 1 node left Node* merge_sort(Node* head) { if (head == nullptr || head->next == nullptr) { return head; } Node* mid = get_mid(head); Node* next_to_mid = mid->next; mid->next = nullptr; Node* left = merge_sort(head); Node* right = merge_sort(next_to_mid); Node* sorted_merge = merge(left, right); return sorted_merge; } // Function to print the list elements void display() { Node* p = head; while (p != nullptr) { std::cout << p->data << " "; p = p->next; } std::cout << std::endl; }};// Function to get the difference listLinkedList get_difference(Node* p1, Node* p2) { LinkedList difference_list; // Scan the lists while (p1 != nullptr && p2 != nullptr) { // Condition to check if the data of both pointers are the same, then move ahead if (p2->data == p1->data) { p1 = p1->next; p2 = p2->next; } else if (p2->data < p1->data) { // Condition to check if the data of the second pointer is smaller than the first, then move the second pointer ahead p2 = p2->next; } else { // Condition when the data of the first pointer is greater than the second, then append into the difference list and move difference_list.append(p1->data); p1 = p1->next; } } // If the end of list2 is reached, there may be some nodes in List 1 left to be scanned, // they all will be inserted in the difference list while (p1 != nullptr) { difference_list.append(p1->data); p1 = p1->next; } return difference_list;}int main() { // Linked List 1 LinkedList list1; list1.append(2); list1.append(6); list1.append(8); list1.append(1); // Linked List 2 LinkedList list2; list2.append(4); list2.append(1); list2.append(9); // Sort both linked lists list1.head = list1.merge_sort(list1.head); list2.head = list2.merge_sort(list2.head); // Get the difference list LinkedList result = get_difference(list1.head, list2.head); if (result.head) { result.display(); } else { std::cout << "Lists are equal" << std::endl; } return 0;} |
Java
class Node { int data; Node next; Node(int data) { this.data = data; this.next = null; }}class LinkedList { Node head; LinkedList() { head = null; } // Function to insert a node at the end of Linked List void append(int data) { Node newNode = new Node(data); if (head == null) { head = newNode; } else { Node current = head; while (current.next != null) { current = current.next; } current.next = newNode; } } // Function to find the middle node of the Linked List Node getMid(Node head) { if (head == null) { return head; } Node slow = head; Node fast = head; while (fast.next != null && fast.next.next != null) { slow = slow.next; fast = fast.next.next; } return slow; } // Recursive method to merge two halves after sorting Node merge(Node left, Node right) { if (left == null) { return right; } if (right == null) { return left; } Node result; if (left.data <= right.data) { result = left; result.next = merge(left.next, right); } else { result = right; result.next = merge(left, right.next); } return result; } // Recursive method to divide the list into two halves until 1 node left Node mergeSort(Node head) { if (head == null || head.next == null) { return head; } Node mid = getMid(head); Node nextToMid = mid.next; mid.next = null; Node left = mergeSort(head); Node right = mergeSort(nextToMid); return merge(left, right); } // Function to print the list elements void display() { Node current = head; while (current != null) { System.out.print(current.data + " "); current = current.next; } System.out.println(); } // Function to get the difference list static LinkedList getDifference(Node p1, Node p2) { LinkedList differenceList = new LinkedList(); // Scan the lists while (p1 != null && p2 != null) { // Condition to check if the data of both pointers are the same, then move ahead if (p2.data == p1.data) { p1 = p1.next; p2 = p2.next; } else if (p2.data < p1.data) { // Condition to check if the data of the second pointer is smaller than the first, then move the second pointer ahead p2 = p2.next; } else { // Condition when the data of the first pointer is greater than the second, then append into the difference list and move differenceList.append(p1.data); p1 = p1.next; } } // If the end of list2 is reached, there may be some nodes in List 1 left to be scanned, they all will be inserted in the difference list while (p1 != null) { differenceList.append(p1.data); p1 = p1.next; } return differenceList; }}public class Main { public static void main(String[] args) { // Linked List 1 LinkedList list1 = new LinkedList(); list1.append(2); list1.append(6); list1.append(8); list1.append(1); // Linked List 2 LinkedList list2 = new LinkedList(); list2.append(4); list2.append(1); list2.append(9); // Sort both the linked lists list1.head = list1.mergeSort(list1.head); list2.head = list2.mergeSort(list2.head); // Get the difference list LinkedList result = LinkedList.getDifference(list1.head, list2.head); if (result.head != null) { result.display(); } else { System.out.println("Lists are equal"); } }} |
Python3
# Python implementation to create# a difference Linked List of # two Linked Lists# Node of the Linked Listclass Node: def __init__(self, data): self.data = data self.next = None# Linked Listclass linked_list: def __init__(self): self.head = None # Function to insert a node # at the end of Linked List def append(self, data): temp = Node(data) if self.head == None: self.head = temp else: p = self.head while p.next != None: p = p.next p.next = temp # Function to find the middle # node of the Linked List def get_mid(self, head): if head == None: return head slow = fast = head while fast.next != None \ and fast.next.next != None: slow = slow.next fast = fast.next.next return slow # Recursive method to merge the # two half after sorting def merge(self, l, r): if l == None:return r if r == None:return l if l.data<= r.data: result = l result.next = \ self.merge(l.next, r) else: result = r result.next = \ self.merge(l, r.next) return result # Recursive method to divide the # list into two half until 1 node left def merge_sort(self, head): if head == None or head.next == None: return head mid = self.get_mid(head) next_to_mid = mid.next mid.next = None left = self.merge_sort(head) right = self.merge_sort(next_to_mid) sorted_merge = self.merge(left, right) return sorted_merge # Function to print the list elements def display(self): p = self.head while p != None: print(p.data, end =' ') p = p.next print()# Function to get the difference listdef get_difference(p1, p2): difference_list = linked_list() # Scan the lists while p1 != None and p2 != None: # Condition to check if the # Data of the both pointer are # same then move ahead if p2.data == p1.data: p1 = p1.next p2 = p2.next # Condition to check if the # Data of the first pointer is # greater than second then # move second pointer ahead elif p2.data<p1.data: p2 = p2.next # Condition when first pointer # data is greater than the # second pointer then append # into the difference list and move else: difference_list.append(p1.data) p1 = p1.next # If end of list2 is reached, # there may be some nodes in # List 1 left to be scanned, # they all will be inserted # in the difference list if p2 == None: while p1: difference_list.append(p1.data) p1 = p1.next return difference_list# Driver Codeif __name__ == '__main__': # Linked List 1 list1 = linked_list() list1.append(2) list1.append(6) list1.append(8) list1.append(1) # Linked List 2 list2 = linked_list() list2.append(4) list2.append(1) list2.append(9) # Sort both the linkedlists list1.head = list1.merge_sort( list1.head ) list2.head = list2.merge_sort( list2.head ) # Get difference list result = get_difference( list1.head, list2.head ) if result.head: result.display() # if difference list is empty, # then lists are equal else: print('Lists are equal') |
Output
2 6 8
Time complexity: O(M Log M + N Log N).
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