LinkList_reverse.java

import java.util.LinkedList;
import java.util.jar.Attributes.Name;

//ek LL di hai use sirf reverse karna hai
// [1 , 2 , 3 , 4 ] ...
// [4 , 3 , 2 , 1 ]..
//by iterate 
//isme ham 3 verable banayenge (prev , curr , next);;
//curr ka next ko hame prev banana hai;;--> curr.next=prev;
//

public class LinkList_reverse {
 node head;
 private int size; // private size ka int banaya

 LinkList_reverse() {
 this.size = 0; // size ko initialize 0 se kr diya ;;;
 }

 class node { // node cclass bana li hamne
 int data;
 node next;

 node(int data) { // CONSTRUCTOR bana liya
 this.data = data;
 this.next = null;
 size++;

 }

 }

 // ADD--1.FIRST...2.LAST
 public void addfirst(int data) {
 node newnode = new node(data);
 if (head == null) {
 head = newnode;
 return;
 }

 newnode.next = head;
 head = newnode;

 }

 // ADD LAST
 public void addlast(int data) {
 node newnode = new node(data);
 if (head == null) {
 head = newnode;
 return;
 }
 node currnode = head;
 while (currnode.next != null) {
 currnode = currnode.next;

 }
 currnode.next = newnode;

 }

 // print
 public void printlist() {
 if (head == null) {
 System.out.println(" LL is empty");
 return;
 }
 node currnode = head;
 while (currnode != null) {
 System.out.print(currnode.data + "-->");
 currnode = currnode.next;

 }
 System.out.println("null");
 }

 // DELETE
 // first ko delete karna hai to first ke next ko head banana hoga
 // last ko agr delete karna hai ..to next-next karna hai aur jaise hi second
 // last node tak pohochenge .
 // to second last node ko null bana lenge
 // delete first
 public void deletefirst() {
 if (head == null) {
 System.out.println("LL is empty");
 return;

 }
 size--; // delete hone ke bad size ko kam karna padega
 head = head.next; // head.next ko head banaya to head carbej ho gya
 }

 public void deletelast() {
 if (head == null) {
 System.out.println("LL is empty");
 return;
 }
 size--; //// delete hone ke bad size ko kam karna padega
 node seclast = head; // head ko sechead banaya
 node lastnode = head.next; // head next ko last node banaaya

 if (head.next == null) { // jisme LL me ek hi node hoga //next karte wakt null ka next null nahi ho sakta
 head = null;
 return;
 }

 while (lastnode.next != null) { // jabtak last node null nahi ho jata
 lastnode = lastnode.next; // lastnode next ko last node me dalneka
 seclast = seclast.next; // aur seclast node ke next ko sec last me dalneka jo ki head banaya hai

 }
 seclast.next = null;
 // lastnode = null;

 }

 public int getsize() {
 return size;
 }

 public void reverseiterate() {
 if (head == null || head.next == null) {
 return;

 }
 node prenode = head; // head ko prenode kr diya
 node currnode = head.next; // head ke next ko currnode kr diya
 while (currnode != null) { // jab tk currnode null nahi ho jyata
 node nextnode = currnode.next; // currnode ke next ko nextnode kr diya;;
 currnode.next = prenode; // prenode ko currnode ke next me dalne ka ;;;

 // uodate
 prenode = currnode; // simply aage ka ek kadam pichhe aayega ;;; currrnode ko prenode matlan ek
 // kadam pichhe
 currnode = nextnode; // nextnode ko currnode

 }
 head.next = null; // last me head ka next null hoga
 head = prenode; // head hoga prenode;;;
 }

 public node reverserecursive(node head) {
 if (head == null || head.next == null) {
 return head;
 }
 node newhead = reverserecursive(head.next);
 head.next.next = head;
 head.next = null;
 return newhead;

 }

 public static void main(String[] args) {
 LinkList_reverse list = new LinkList_reverse();
 list.addfirst(1);
 list.addfirst(2);
 list.addfirst(3);
 list.addfirst(4);
 list.printlist();
 // list.reverseiterate();
 // list.printlist();
 list.head = list.reverserecursive(list.head);
 list.printlist();
 }

}

// ye hame iteratively reverse kiya