Answers for "linked list reverse"

reverse linked list in java to get both head and tail

/*
public class ListNode {
    public int val;
    public ListNode next;
    public ListNode(int x) { val = x; next = null; }
}
*/

public static ListNode[] reverse_linked_list(ListNode head) {

        ListNode prev = null;
        ListNode current = head;
        ListNode next;

        ListNode tail = head;

        while (current != null) {

            next = current.next;
            current.next = prev;
            prev = current;
            current = next;
        }

        head = prev;

        ListNode[] result = {head, tail};

        return result;
}

how to reverse a linked ist

class LinkedList { 
  
    static Node head; 
  
    static class Node { 
  
        int data; 
        Node next; 
  
        Node(int d) 
        { 
            data = d; 
            next = null; 
        } 
    } 
  
    /* Function to reverse the linked list */
    Node reverse(Node node) 
    { 
        Node prev = null; 
        Node current = node; 
        Node next = null; 
        while (current != null) { 
            next = current.next; 
            current.next = prev; 
            prev = current; 
            current = next; 
        } 
        node = prev; 
        return node; 
    } 
  
    // prints content of double linked list 
    void printList(Node node) 
    { 
        while (node != null) { 
            System.out.print(node.data + " "); 
            node = node.next; 
        } 
    } 
  
    public static void main(String[] args) 
    { 
        LinkedList list = new LinkedList(); 
        list.head = new Node(85); 
        list.head.next = new Node(15); 
        list.head.next.next = new Node(4); 
        list.head.next.next.next = new Node(20); 
  
        System.out.println("Given Linked list"); 
        list.printList(head); 
        head = list.reverse(head); 
        System.out.println(""); 
        System.out.println("Reversed linked list "); 
        list.printList(head); 
    } 
}

reverse linked list by k

//Iterative program in C++ to reverse a linked list in groups of k

//	(just before end of 2nd iteration of outer loop) [ 1->2->3->4->5->NULL ]
// 1 <- 2    3 <- 4  5 ->NULL   (k=2)
   ^		 ^		 ^
   |		 |		 |
prev_tail temp_head walker

void reverse_by_k(Node **head,int k){
    Node* temp_head = *head,*walker = *head,*prev_tail = NULL;
    while(walker){
        int i=0;
        Node *temp = NULL,*prev = NULL;
        //initialize temporary head to set previous tail later
        temp_head = walker;
        
        //reverse group of k nodes
        while(i<k && walker){
            temp = walker->next;
            walker->next = prev;
            prev = walker;
            walker = temp;
            i++;
        }
        
        if(prev_tail){
            //previous tail has to point to temporary head of current group
            prev_tail->next = prev;
            prev_tail = temp_head;
        } else{
            prev_tail = *head;
            *head = prev;
        }
    }
}

reverse a linked list

class recursion { 
	static Node head; // head of list 
	static class Node { 
		int data; 
		Node next; 
		Node(int d) 
		{   data = d; 
			next = null; 	} } 
	static Node reverse(Node head) 
	{ 
		if (head == null || head.next == null) 
			return head; 
		/* reverse the rest list and put the first element 
        at the end */
		Node rest = reverse(head.next); 
		head.next.next = head; 
		/* tricky step -- see the diagram */
    	head.next = null; 
		/* fix the head pointer */
		return rest; 
	}  /* Function to print linked list */
	static void print() 
	{ 
		Node temp = head; 
		while (temp != null) { 
			System.out.print(temp.data + " "); 
			temp = temp.next; 
		} 
		System.out.println(); 
	} 
	static void push(int data) 
	{ 
		Node temp = new Node(data); 
		temp.next = head; 
		head = temp; 
	} /* Driver program to test above function*/
public static void main(String args[]) 
{ 
	/* Start with the empty list */
	push(20); 
	push(4); 
	push(15); 
	push(85); 
	System.out.println("Given linked list"); 
	print(); 
	head = reverse(head); 
	System.out.println("Reversed Linked list"); 
	print(); 
} } // This code is contributed by Prakhar Agarwal

Reverse a linked list c++

#include<bits/stdc++.h>
 
using namespace std;
 
struct node {
    int data;
    struct node *next;
};
 
// To create a demo we have to construct a linked list and this 
// function is to push the elements to the list. 
void push(struct node **head_ref, int data) {
    struct node *node;
    node = (struct node*)malloc(sizeof(struct node));
    node->data = data;
    node->next = (*head_ref);
    (*head_ref) = node;
}
 
// Function to reverse the list
void reverse(struct node **head_ref) {
    struct node *temp = NULL;
    struct node *prev = NULL;
    struct node *current = (*head_ref);
    while(current != NULL) {
        temp = current->next;
        current->next = prev;
        prev = current;
        current = temp;
    }
    (*head_ref) = prev;
}
 
// To check our program 
void printnodes(struct node *head) {
    while(head != NULL) {
        cout<<head->data<<" ";
        head = head->next;
    }
}
 
// Driver function
int main() {
    struct node *head = NULL;
    push(&head, 0);
    push(&head, 1);
    push(&head, 8);
    push(&head, 0);
    push(&head, 4);
    push(&head, 10);
    cout << "Linked List Before Reversing" << endl;
    printnodes(head);
    reverse(&head);
    cout << endl;
    cout << "Linked List After Reversing"<<endl;
    printnodes(head);
    return 0;
}

linked list reverse

// using iterative method to reverse linked list in JavaScript
// time complexity: O(n) & space complexity: O(1)
reverse() {
      if (!this.head.next) {
        return this.head;
      }
      
      let prevNode = null;
      let currNode = this.head;
      let nextNode = this.head;
      while(nextNode){
        nextNode = currNode.next;
        currNode.next = prevNode;
        prevNode = currNode;
        currNode = nextNode;
      }
      this.head = prevNode;
      return this.printList();
    }