JAVA

linked list reverse

//iterative
public ListNode ReverseList(ListNode head) 
{
    ListNode prev = null;
    var current= head;

    while(current!=null)
    {
        var next = current.next;
        current.next=prev;
        prev =current;
        current=next;
    }
    return prev;
}
// recursive
public ListNode ReverseList(ListNode head) 
{
    if(head==null || head.next == null)
        return head;

    var t2 = ReverseList(head.next);
    head.next.next = head;
    head.next = null;

    return t2;
}

reversing the linked list

// Java program for reversing the linked list
 
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;
        }
    }
 
    // Driver Code
    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);
    }
}
 
// This code has been contributed by Mayank Jaiswal

Reverse a Linked List

	    /* Before changing next pointer of current node,
        store the next node */
        next = curr -> next
        /*  Change next pointer of current node */
        /* Actual reversing */
        curr -> next = prev
        /*  Move prev and curr one step ahead */
        prev = curr
        curr = next

reverse a linked list

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode() {}
 *     ListNode(int val) { this.val = val; }
 *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
 * }
 */
class Solution {
    public ListNode reverseList(ListNode head) {
        
        ListNode current = head;
        ListNode prev = null;
        ListNode next = null;
        
        if(head == null)
        {
            return head;
        }
        while(current != null)
        {
            next = current.next;
            current.next = prev;
            prev = current;
            current = next;
        }
        return prev;
    }
}

Revese a Linked List

LinkedList<Integer> ll = new LinkedList<>();

ll.add(1);
ll.add(2);
ll.add(3);
System.out.println(ll);

LinkedList<Integer> ll1 = new LinkedList<>();

ll.descendingIterator().forEachRemaining(ll1::add);

System.out.println(ll1);

Reverse a Linked List

void reverse()
	{
		node* current, * prev, * temp;
		current = head;
		prev = NULL;
		while (current != NULL)
		{
			temp = current->next;
			current->next = prev;
			prev = current;
			current = temp;
		}
		head = prev;
	}