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Python/C/C++/JAVA

Advanced Practice Programs with Code and Concept

By D.S
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Reverse a Linked List

Reversing a linked list is a fundamental operation in computer science and programming. It involves changing the direction of the pointers in each node so that the last node becomes the first, the second-to-last node becomes the second, and so on, effectively flipping the order of the list. This operation is essential for various algorithms and data structures. Below, you'll find implementations of linked list reversal in different programming languages such as C, C++, Python, and Java.

(a.) C Code

#include <stdio.h>
      #include <stdlib.h>
      
      struct Node {
          int data;
          struct Node* next;
      };
      
      void insert(struct Node** head_ref, int new_data) {
          struct Node* new_node = (struct Node*)malloc(sizeof(struct Node));
          new_node->data = new_data;
          new_node->next = (*head_ref);
          (*head_ref) = new_node;
      }
      
      void printList(struct Node* node) {
          while (node != NULL) {
              printf("%d ", node->data);
              node = node->next;
          }
          printf("
");
      }
      
      void reverse(struct Node** head_ref) {
          struct Node* prev = NULL;
          struct Node* current = *head_ref;
          struct Node* next = NULL;
          while (current != NULL) {
              next = current->next;
              current->next = prev;
              prev = current;
              current = next;
          }
          *head_ref = prev;
      }
      
      int main() {
          struct Node* head = NULL;
          insert(&head, 1);
          insert(&head, 2);
          insert(&head, 3);
          insert(&head, 4);
          printf("Original linked list: 
");
          printList(head);
          reverse(&head);
          printf("Reversed linked list: 
");
          printList(head);
          return 0;
      }
Output:-
Original linked list: 4 3 2 1 Reversed linked list: 1 2 3 4

(b.) C++ Code

#include <iostream>
      using namespace std;
      
      class Node {
      public:
          int data;
          Node* next;
      };
      
      void insert(Node** head_ref, int new_data) {
          Node* new_node = new Node();
          new_node->data = new_data;
          new_node->next = (*head_ref);
          (*head_ref) = new_node;
      }
      
      void printList(Node* node) {
          while (node != NULL) {
              cout << node->data << " ";
              node = node->next;
          }
          cout << endl;
      }
      
      void reverse(Node** head_ref) {
          Node* prev = NULL;
          Node* current = *head_ref;
          Node* next = NULL;
          while (current != NULL) {
              next = current->next;
              current->next = prev;
              prev = current;
              current = next;
          }
          *head_ref = prev;
      }
      
      int main() {
          Node* head = NULL;
          insert(&head, 1);
          insert(&head, 2);
          insert(&head, 3);
          insert(&head, 4);
          cout << "Original linked list: " << endl;
          printList(head);
          reverse(&head);
          cout << "Reversed linked list: " << endl;
          printList(head);
          return 0;
      }
Output:-
Original linked list: 4 3 2 1 Reversed linked list: 1 2 3 4

(c.) Python Code

class Node:
    def __init__(self, data):
        self.data = data
        self.next = None

class LinkedList:
    def __init__(self):
        self.head = None

    def insert(self, new_data):
        new_node = Node(new_data)
        new_node.next = self.head
        self.head = new_node

    def printList(self):
        temp = self.head
        while temp:
            print(temp.data, end=" ")
            temp = temp.next
        print()

    def reverse(self):
        prev = None
        current = self.head
        while current:
            next = current.next
            current.next = prev
            prev = current
            current = next
        self.head = prev

llist = LinkedList()
llist.insert(1)
llist.insert(2)
llist.insert(3)
llist.insert(4)
print("Original linked list:")
llist.printList()
llist.reverse()
print("Reversed linked list:")
llist.printList()
Output:-
Original linked list: 4 3 2 1 Reversed linked list: 1 2 3 4

(d.) Java Code

class Node {
      int data;
      Node next;
  
      Node(int d) {
          data = d;
          next = null;
      }
  }
  
  class LinkedList {
      Node head;
  
      void insert(int data) {
          Node new_node = new Node(data);
          new_node.next = head;
          head = new_node;
      }
  
      void printList() {
          Node temp = head;
          while (temp != null) {
              System.out.print(temp.data + " ");
              temp = temp.next;
          }
          System.out.println();
      }
  
      void reverse() {
          Node prev = null;
          Node current = head;
          Node next = null;
          while (current != null) {
              next = current.next;
              current.next = prev;
              prev = current;
              current = next;
          }
          head = prev;
      }
  
      public static void main(String[] args) {
          LinkedList llist = new LinkedList();
          llist.insert(1);
          llist.insert(2);
          llist.insert(3);
          llist.insert(4);
          System.out.println("Original linked list:");
          llist.printList();
          llist.reverse();
          System.out.println("Reversed linked list:");
          llist.printList();
      }
  }
Output:-
Original linked list: 4 3 2 1 Reversed linked list: 1 2 3 4

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