Question

Write java code to reverse a linked list. Fill in reverseLists()

ReverseLinkedList.java

package mid;

public class ReverseLinkedList {

    private static class ListNode {

        int val;

        ListNode next;

        ListNode() {

        }

        ListNode(int val) {

            this.val = val;

        }

        ListNode(int val, ListNode next) {

            this.val = val;

            this.next = next;

        }

    }

    public static void printList(ListNode l1) {

        ListNode cur = l1;

        while(cur != null) {

            System.out.println(cur.val);

            cur = cur.next;

        }

    }

    public static ListNode reverseLists(ListNode h1) {

    }

    public static void main(String[] args) {

        ListNode l1_4 = new ListNode(4);

        ListNode l1_3 = new ListNode(3, l1_4);

        ListNode l1_2 = new ListNode(2, l1_3);

        ListNode l1_1 = new ListNode(1, l1_2);

        ListNode h1 = l1_1;

        System.out.println("list is:");

        printList(h1);

        ListNode h2 = reverseLists(h1);

        System.out.println("Reversed list is:");

        printList(h2);

    }

}

Answer 1

public class Main {

    private static class ListNode {

        int val;

        ListNode next;

        ListNode() {

        }

        ListNode(int val) {

            this.val = val;

        }

        ListNode(int val, ListNode next) {

            this.val = val;

            this.next = next;

        }

    }
//to diplay the list
    public static void printList(ListNode l1) {

        ListNode cur = l1;

        while(cur != null) {//iterating until null value

            System.out.println(cur.val);//printing node value

            cur = cur.next;

        }

    }
//-----------------------------------------------------------
//reversing the list by sending the header as parameter to it
    public static ListNode reverseLists(ListNode h1) {

    ListNode prev = null;
    ListNode current = h1;
        ListNode next = null;
        while (current != null) { //iterating until null
            //swaping the nodes in list
            next = current.next;
            current.next = prev;
            prev = current;
            current = next;
        }
        h1= prev;
        return h1; //returning the header
      
    }
//-------------------------------------------------------------------------
    public static void main(String[] args) {
    //CREATING LINKED LIST

        ListNode l1_4 = new ListNode(4);

        ListNode l1_3 = new ListNode(3, l1_4);

        ListNode l1_2 = new ListNode(2, l1_3);

        ListNode l1_1 = new ListNode(1, l1_2);

        ListNode h1 = l1_1;

        System.out.println("list is:");
  
        printList(h1);

       ListNode h2 = reverseLists(h1);

        System.out.println("Reversed list is:");

        printList(h2);

    }

}

. Fill in reverseLists()