Correct the Random Pointer in Doubly Linked List
Given a doubly linked list having exactly one of the node pointing to a random node in the list, the task is to correct this random pointer in the doubly linked list, such that it points to the expected node.
Examples:
Input:
Output:
Explanation: 2’s next pointer has been corrected to point to 3. Earlier it was pointing to 1, which was incorrect.
Approach: This can be achieved by simply iterating the list and checking the individual pointers.
Below is the implementation for the above approach:
C++
// C++ program to Correct// the Random Pointer in Doubly Linked List#include<iostream>using namespace std; // Node of a doubly linked listclass Node{ public: int data; // Pointer to next node in DLL Node *next; // Pointer to previous node in DLL Node *prev; Node():prev(NULL),next(NULL){} Node(int data):data(data),prev(NULL),next(NULL){}};class doublell{ public: Node *head; // Function to append node in the DLL void appendNode(Node *n) { Node *temp=head; if(temp==NULL) { head=n; } else { while(temp->next!=NULL) { temp=temp->next; } temp->next=n; n->prev=temp; } } // Function to print the DLL void print() { Node *temp=head; while(temp!=NULL) { cout<<temp->data<<"->"; temp=temp->next; } cout<<endl; } // Function to print reverse of the DLL void printReverse() { Node *temp=head; while(temp->next!=NULL) { temp=temp->next; } while(temp!=NULL) { cout<<temp->data<<" ->"; temp=temp->prev; } cout<<endl; } // Function to correct the random pointer void correctPointer() { if(!head) { return; } Node *temp=head; while(temp->next!=NULL) { if(temp->next->prev!=temp) { temp->next->prev=temp; } temp=temp->next; } }};// Driver Codeint main() { // Creating a DLL doublell ll; ll.head = new Node(1); ll.head->next = new Node(2); ll.head->next->prev = ll.head; ll.head->next->next = new Node(3); ll.head->next->next->prev =ll.head; ll.head->next->next->next = new Node(4); ll.head->next->next->next->prev = ll.head->next->next; cout << "\nIncorrect Linked List: "; ll.print(); ll.printReverse(); ll.correctPointer(); cout << "\nCorrected Linked List: "; ll.print(); ll.printReverse(); return 0; } |
Java
// Java program to Correct// the Random Pointer in Doubly Linked Listclass GFG {// Node of a doubly linked liststatic class node { int data; // Pointer to next node in DLL node next; // Pointer to previous node in DLL node prev;};// Function to allocate nodestatic node newNode(int data){ node temp = new node(); temp.data = data; temp.next = temp.prev = null; return temp;}// Function to correct the random pointerstatic void correctPointer(node head){ if (head == null) return; node temp = head; // if head->next's previous is not // pointing to head itself, // change it. if (head.next != null && head.next.prev != head) { head.next.prev = head; return; } // If head's previous pointer is incorrect, // change it. if (head.prev != null) { head.prev = null; return; } // Else check for remaining nodes. temp = temp.next; while (temp != null) { // If node.next's previous pointer is // incorrect, change it. if (temp.next != null && temp.next.prev != temp) { temp.next.prev = temp; return; } // Else If node.prev's next pointer is // incorrect, change it. else if (temp.prev != null && temp.prev.next != temp) { temp.prev.next = temp; return; } System.out.print(""); // Else iterate on remaining. temp = temp.next; }}// Function to print the DLLstatic void printList(node head){ node temp = head; while (temp != null) { System.out.print(temp.data + " ("); // If prev pointer is null, print -1. System.out.print((temp.prev != null ? temp.prev.data: -1) + ") "); temp = temp.next; } System.out.print("\n");}// Driver Codepublic static void main(String[] args){ // Creating a DLL node head = newNode(1); head.next = newNode(2); head.next.prev = head; head.next.next = newNode(3); head.next.next.prev = head; head.next.next.next = newNode(4); head.next.next.next.prev = head.next.next; System.out.print("\nIncorrect Linked List: "); printList(head); correctPointer(head); System.out.print("\nCorrected Linked List: "); printList(head);}}// This code is contributed by Princi Singh |
Python3
# Python3 program to Correct the# Random Pointer in Doubly Linked Listclass Node: def __init__(self, data): self.data = data self.prev = None self.next = None# Function to correct the random pointerdef correctPointer(head): if head == None: return temp = head # if head.next's previous is not # pointing to head itself, change it. if (head.next != None and head.next.prev != head): head.next.prev = head return # If head's previous pointer is # incorrect, change it. if head.prev != None: head.prev = None return # Else check for remaining nodes. temp = temp.next while temp != None: # If node.next's previous pointer # is incorrect, change it. if (temp.next != None and temp.next.prev != temp): temp.next.prev = temp return # Else If node.prev's next pointer # is incorrect, change it. elif (temp.prev != None and temp.prev.next != temp): temp.prev.next = temp return # Else iterate on remaining. temp = temp.next # Function to print the DLLdef printList(head): temp = head while temp != None: print(temp.data, "(", end = "") # If prev pointer is null, print -1. if temp.prev == None: print(-1, end = ") ") else: print(temp.prev.data, end = ") ") temp = temp.next print()# Driver Codeif __name__ == "__main__": # Creating a DLL head = Node(1) head.next = Node(2) head.next.prev = head head.next.next = Node(3) head.next.next.prev = head head.next.next.next = Node(4) head.next.next.next.prev = head.next.next print("Incorrect Linked List:", end = " ") printList(head) correctPointer(head) print("\nCorrected Linked List:", end = " ") printList(head)# This code is contributed # by Rituraj Jain |
C#
// C# program to Correct the // Random Pointer in Doubly Linked Listusing System;class GFG {// Node of a doubly linked listclass node { public int data; // Pointer to next node in DLL public node next; // Pointer to next node in DLL public node prev;};// Function to allocate nodestatic node newNode(int data){ node temp = new node(); temp.data = data; temp.next = temp.prev = null; return temp;}// Function to correct the random pointerstatic void correctPointer(node head){ if (head == null) return; node temp = head; // if head->next's previous is not // pointing to head itself, // change it. if (head.next != null && head.next.prev != head) { head.next.prev = head; return; } // If head's previous pointer is incorrect, // change it. if (head.prev != null) { head.prev = null; return; } // Else check for remaining nodes. temp = temp.next; while (temp != null) { // If node.next's previous pointer is // incorrect, change it. if (temp.next != null && temp.next.prev != temp) { temp.next.prev = temp; return; } // Else If node.prev's next pointer // is incorrect, change it. else if (temp.prev != null && temp.prev.next != temp) { temp.prev.next = temp; return; } Console.Write(""); // Else iterate on remaining. temp = temp.next; }}// Function to print the DLLstatic void printList(node head){ node temp = head; while (temp != null) { Console.Write(temp.data + " ("); // If prev pointer is null, print -1. Console.Write((temp.prev != null ? temp.prev.data: -1) + ") "); temp = temp.next; } Console.Write("\n");}// Driver Codepublic static void Main(String[] args){ // Creating a DLL node head = newNode(1); head.next = newNode(2); head.next.prev = head; head.next.next = newNode(3); head.next.next.prev = head; head.next.next.next = newNode(4); head.next.next.next.prev = head.next.next; Console.Write("\nIncorrect Linked List: "); printList(head); correctPointer(head); Console.Write("\nCorrected Linked List: "); printList(head);}}// This code is contributed by PrinciRaj1992 |
Javascript
// Node of a doubly linked listclass Node { constructor(data) { this.data = data; this.prev = null; this.next = null; }}class doublell { constructor() { this.head = null; } // Function to append node in the DLL appendNode(n) { let temp = this.head; if (!temp) { this.head = n; } else { while (temp.next) { temp = temp.next; } temp.next = n; n.prev = temp; } } // Function to print the DLL in a single line print() { let temp = this.head; let result = ""; while (temp) { result += temp.data + " -> "; temp = temp.next; } console.log(result); } // Function to print reverse of the DLL in a single line printReverse() { let temp = this.head; while (temp && temp.next) { temp = temp.next; } let result = ""; while (temp) { result += temp.data + " -> "; temp = temp.prev; } console.log(result); } // Function to correct the random pointer correctPointer() { if (!this.head) { return; } let temp = this.head; while (temp.next) { if (temp.next.prev !== temp) { temp.next.prev = temp; } temp = temp.next; } }}// Creating a DLLconst ll = new doublell();ll.head = new Node(1);ll.head.next = new Node(2);ll.head.next.prev = ll.head;ll.head.next.next = new Node(3);ll.head.next.next.prev = ll.head;ll.head.next.next.next = new Node(4);ll.head.next.next.next.prev = ll.head.next.next;console.log("\nIncorrect Linked List: ");ll.print();ll.printReverse();ll.correctPointer();console.log("\nCorrected Linked List: ");ll.print();ll.printReverse(); |
Output
Incorrect Linked List: 1 (-1) 2 (1) 3 (1) 4 (3) Corrected Linked List: 1 (-1) 2 (1) 3 (2) 4 (3)
Time Complexity: O(n)
Auxiliary Space: O(n)
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