In order to reverse the linked list, you need to iterate through the list, and at each step, we need to reverse the link like after the first iteration head will point to null and the next element will point to head. System.out.println("The items in the reversed linked list are"); In this tutorial, we understand the concept of reversing the linked list through definition, the logic on which the linked list is reversed is explained. If the list consisting of just one node needs to be reversed, then following the above two steps can complete the task. System.out.println("The items in the linked list that needs to be reversed are"); The method descendingIterator() returns an Iterator object with reverse order. data1 = d1; To reverse a LinkedList recursively we need to divide the LinkedList into two parts: head and remaining. // The contents of linked list are printed { The above steps are repeated until the ptrB is pointing to null which means that all the nodes in the original list are reversed. //Last node is marked as head Here, we need to create a StringBuilder from the String input and then call the reverse() method: Example: For linked list 20->40->60->80, the reversed linked list is 80->60->40->20. } For Linkedlist, we just need to replace ArrayList with LinkedList in “List mylist = new ArrayList ();”. list.head1 = new Node(20); System.out.print(node1.data1 + " "); To reverse an ArrayList in Java, you can use java.util.Collections class, or use any looping technique to traverse the elements and create another list with elements added in reverse order. public static void main(String[] args) PayPal Java SDK Complete Example – How to Invoke PayPal Authorization REST API using Java Client? } It is defined in Stream interface which is present in java.util package. { In this article, we will write a simple program to reverse a Stack using recursion. This method reverses a List by modifying the list in-place i.e. The purpose of using this pointer is for backup so that to make sure the list is not lost ahead of ptrB, otherwise, it causes loss of references ahead of ptrB. 2. Here we discuss the examples of Reverse Linked List in Java along with the codes and outputs. The basic idea is to create an empty ArrayList and add elements of the original list to it by iterating the list in the reverse order. } list.head1.nex.nex = new Node(40); To Collections.sort() method, you can pass LinkedList or Vector objects similar to the ArrayList. methods, which should behave like a reversed list. It doesn’t create a new list object instead straightway modifies the original copy. Note: If you just want to iterate the list in reverse order and do not want to change the original list by reversing it, have a look at how to iterate the ArrayList in reverse order example. In another method of array reverse in Java, an array can be converted into an ArrayList, after which a specific code can be used for reversing the ArrayList. } File: StringFormatter.java The reversing of the linked list begins by initializing the ptrA to Null. Write a singleton class. If the node current is null, then it is returned. //previous node is updated with next 3. } This article is contributed by Mohit Gupta. return head1; while (node1 != null) If the next element of the current node is null, it indicates it is the last node in the list. head1 = current; It returns a stream sorted according to the natural order. previous = curr; You may also have a look at the following articles to learn more –, All in One Software Development Bundle (600+ Courses, 50+ projects). List list = new List(); 1. } Find out middle index where sum of both ends are equal. sort() method for sorting ArrayList.The Collections.reverse() method also accepts a List, so you not only can reverse ArrayList but also any other implementation of List interface e.g. The idea is to get a stream of all valid indices of the list in reverse order and map each index to its value in the list, and finally collect the elements in an ArrayList. it doesn’t require an extra list. node1 = previous; In Java8 How to Shuffle, Reverse, Copy, Rotate and Swap List using Collection APIs? 1) Divide the list in two parts - first node and rest of the linked list. { return node1; This is a guide to Reverse Linked List in Java. Guava’s Lists.reverse () method creates a view of the specified list in reversed order. Write a program to reverse a string using recursive algorithm. It must be set to null because ptrA will be the tail node after reverse the linked list. Each node in a linked list having reference to next node. Reverse single linked list using non recursive or iterative algorithm in java. Reverse ArrayList using java.util.Collections ; There can be two solution to reverse a linked list in java. In this post, we will see how to reverse an ArrayList in Java by creating a copy of it in reverse order without altering the ordering of elements in the original list. return head1; If the list size is equal to or more than 18, it uses ListIterator to swap the elements and reverse the list. Check if given Linked List is a Circular Linked List or not. { //Function to reverse the list is called here { today we are going to learn the concept of reversing a LinkedList in Java.Before we move to learn how to reverse a LinkedList in Java, let me tell you that LinkedList is a data structure where every data element is in the form of a node and each node contains the address of the next node. The algorithm begins by considering the node current as of the head. Let's understand the problem statement in simple words, You are given a Singly linked list, print the linked list in reverse way, from end to start. reverse(nex1, current); l.printL(head1); Reverse Singly Linked List is one of the best all time favorite interview question for me. Node nex; Since the returned list is backed by the original list, changes in the returned list are reflected in this list, and vice-versa. 4) Fix head pointer Node(int d1) A linked list can be reversed in java using two algorithms. Here’s is another way in Java 8 and above that uses Collections.reverse() along with Stream API, and Collectors.collectingAndThen() method which collects elements in the reversed order: We can also use Java 8 Streams to reverse a List. Write a Java program to reverse a given linked list. Following example reverses an array list by using Collections.reverse(ArrayList)method. } Java Stream interface provides two methods for sorting the list: sorted() method. int data1; Queue implementation in java. Find out duplicate number between 1 to N numbers. Single linked list is shown in Fig 1, the head is located at node 1. Reversing an ArrayList or LinkedList. list.printL(head1); They are: Start Your Free Software Development Course, Web development, programming languages, Software testing & others. So we will use ptrC as a backup to the ahead list of ptrB before pointing ptrB’s next to ptrA. I remember asking the same questions to interviewer in different way. node1 = node1.nex; nex = null; static Node head1; © 2020 - EDUCBA. //nex is updated The next of ptrB’s is pointed to ptrA and this is how the existing link of pointers is reversed. { Step 2: Let’s initialize them as currentNode = head, previousNode = null and nextNode = null . Java Basic: Exercise-121 with Solution. To reverse a list using recursion, we pop the very first item from the list in each recursive call and re-add them during the traceback process. THE CERTIFICATION NAMES ARE THE TRADEMARKS OF THEIR RESPECTIVE OWNERS. That’s all about reverse a linked list in java. Node curr = node1; if (current.nex == null) { public static void main(String[] args) we are not using loop constructs like a while, for etc, and we only use the following ADT functions on Stack reverse() method reverses the original list rather than creating a new list with reversed values. List l = new List(); How to reverse Singly Linked List? Print linked list in reverse order in java. These objects have a reverse() method that helps us achieve the desired result. This is the main pointer. the list to be sorted and the Collections.reverseOrder() that reverses the order of an element collection using a Comparator. //The linked list is reversed using this function implement singly linked list in java. static class Node { In which the list is divided into two parts called the first node of the list and the rest of the linked list among which reverse function is called for the rest of the linked list and the rest of the linked list is linked to the first node and the head pointer is fixed. The reference to the list ahead of ptrB will be lost when ptrB’s next is made to point to ptrA. curr.nex = previous; By closing this banner, scrolling this page, clicking a link or continuing to browse otherwise, you agree to our Privacy Policy, Java Training (40 Courses, 29 Projects, 4 Quizzes), 40 Online Courses | 29 Hands-on Projects | 285+ Hours | Verifiable Certificate of Completion | Lifetime Access | 4 Quizzes with Solutions, JavaScript Training Program (39 Courses, 23 Projects, 4 Quizzes), jQuery Training (8 Courses, 5 Projects), Java Interview Question on Multithreading, Multithreading Interview Questions in Java, Software Development Course - All in One Bundle. Hello people! //current.nex node is saved for the recursive call The head of the reversed list must be the last node and hence the last node must be made as head and then return. // Program to reverse an ArrayList in Java, // create a new instance so that original list remains unaffected, Notify of new replies to this comment - (on), Notify of new replies to this comment - (off). 4. digit is then added to the variable reversed after multiplying it by 10. Node previous = null; { This method reverses the elements of an array in the specified list. Related posts. We can avoid this by creating a new ArrayList instance from the returned list as shown below: We know that the Collections.reverse() method modifies the list in-place. Below example shows how to iterate through LinkedList in reverse order. The third place is being pointed by the ptrC. // Content of the reversed linked list are printed Solution. The idea is to extend this class and provide implementations for the get(), set(), remove(), etc. A data structure consisting of nodes where data and a pointer is present in every node and the pointer points to the next node is called a Linked list which is different from an array and when such a linked list is reversed, it is called reversed linked list. Reverse an Int Array Using Java Collections. System.out.println("The items in the linked list that needs to be reversed are"); //Function to reverse the list is called here Do NOT follow this link or you will be banned from the site. print singly linked list in reverse order using recursion. curr = nex; static Node head1; } l.head1 = new Node(30); The specified list may or may not be mutable, but the returned list should be mutable. How to reverse String in Java. // A recursive function to reverse the linked list By iterating through it, you can get the elements in the reverse order. List.add () + List.remove () Another approach to in-place reverse a list is to reorder the elements present in the list using a for-loop which removes an element from the end of the list and insert it into the very beginning, one at a time. Head points to the first element initially. The two algorithms to reverse the linked list are explained, which is an iterative algorithm and the recursive algorithm is explained along with the programming examples to implement the algorithms in java. System.out.println(""); current.nex = previous; nex = curr.nex; { Three-pointers must be initialized which are called ptrA, ptrB and ptrC. }, class List { } { Stream interface provides a sorted() method to sort a list. In this topic, we are going to learn about Reverse Linked List in Java. list.printL(result); In this tutorial we will go over simple way to reverse Linked List in Java.. Let’s get started: Java also offers some mechanisms like StringBuilder and StringBuffer that create a mutable sequence of characters. Sort a Stack using another stack. l.head1.nex.nex.nex = new Node(60); Intersection of two linked lists. descending order using the java.util.Collections.sort() method. Yet another method of array reverse in Java comprises of using the Apache Commons ArrayUtils.reverse () program for the sake of reversing any kind of Java array. } Guava’s Lists.reverse() method creates a view of the specified list in reversed order. Node nex = null; Reverse single linked list in java using non recursive algorithm (examples) Floyd’s cycle detection algorithm to check loop in single linked list ; Reverse singly linked List in pairs in java (example / non-recursive) Find number of times given element exists in single linked list (java/ example) System.out.println(""); In the previous post, we have discussed how to in-place reverse a list in Java. list.head1.nex = new Node(30); ALL RIGHTS RESERVED. In this article, we will write a java program to reverse a singly linked list using recursion. { The idea is to create a copy of the orginal list and then call reverse() method on the copy, rather than the original list itself. How to Read a File line by line using Java 8 Stream – Files.lines() and Files.newBufferedReader() Utils Find length of Linked List in java. In this approach, we will use iterative strategy to reverse linked list with the following steps: Step 1: We create 3 nodes such as currentNode, previousNode and nextNode . Custom reverse without built-in API methods In the previous example, We have seen how we can reverse ArrayList with collections.reverse() method. The idea is to accumulate elements of the given list into a LinkedList using Streams API. The steps below describe how an iterative algorithm works: The steps below describe how a recursive algorithm works: Here are the following examples mention below, Java program to reverse a singly linked list using an iterative algorithm, class List while (node != null) { //The values to be inserted in the list before reversing are given here Pictorial Presentation: Sample Solution: Java Code: Collections.reverse () method reverses the elements of the given ArrayList in linear time i.e it has the time complexity of O (n). } Node reverse(Node current, Node previous) We can avoid this by creating a new ArrayList instance from the returned list as shown below: 1 Arrays class in Java doesn’t have reverse method. current.nex = previous; Here’s even shorten version of above utility method: AbstractList class provides a skeletal implementation of the List interface. void printL(Node node) Java program to reverse a singly linked list using an iterative algorithm. Program: Here is the recursive method to reverse a linked list : Here is complete implementation of Linked List along with the reverse method : Output : Printing nodes … } System.out.println(""); //The values to be inserted in the list before reversing are given here Iterative; Recursive This is the task of ptrA. Remaining points to the next element from the head. Let's see the ways to reverse String in Java. l.head1.nex = new Node(40); Node reverselist(Node node1) Then we get an iterator over the elements in the LinkedList in reverse sequential order using LinkedList.descendingIterator() method and process each element using forEachRemaining() method: The idea here is to use a ListIterator to iterate List in reverse order. ptrB uses ptrA as a reference to point back. list.head1.nex.nex.nex = new Node(50); node = node.nex; You can reverse ArrayList in Java by using the reverse() method of java.util.Collections class. A Linked list contains two things data and the address of the node each node is linked to the next node. This is one of the many utility methods provided by the Collections class e.g. head1 = l.reverselist(head1); l.printL(head1); This method requires two parameters i.e. Implement Queue using Linked List in java. 2) Call reverse for the rest of the linked list. Since the last node in the reversed list is null, initially this pointer will also be null. How to reverse an array list ? We can reverse String using StringBuffer, StringBuilder, iteration etc. Now, the digit contains the last digit of num, i.e. Write a program to create deadlock between two threads. Node(int d1) The second place is being pointed by the ptrB. Method 2: Reverse List using Recursion. Since the returned list is backed by the original list, changes in the returned list are reflected in this list, and vice-versa. Code: class List {static Node head1; static class Node {int data1; Node nex; Node(int d1) {data1 = d1; nex = null;}} // A recursive function to reverse the linked list Node reverse(Node current, Node previous) {//Last node is marked as head if (current.nex == null) {head1 = current; A list can be sorted in reverse order i.e. This website or its third-party tools use cookies, which are necessary to its functioning and required to achieve the purposes illustrated in the cookie policy. If the elements are not comparable, it throws java.lang.ClassCastException. It is the most recommended way to transpose the list both from speed and performance perspective. Example: Input: 10 -> 20 -> 30 -> 40 -> 50 -> null } The given ArrayList can be reversed using Collections.reverse () method. Enter your email address to subscribe to new posts and receive notifications of new posts by email. The first place is being pointed by the ptrA. { void printL(Node node1) The next of ptrB is linked to ptrA because the ptrB which is pointing to the first node becomes the tail node in the reversed list. In this program, while loop is used to reverse a number as given in the following steps: First, the remainder of the num divided by 10 is stored in the variable digit. 1) By StringBuilder / StringBuffer. int data1; It is the simplest method to reverse a List or ArrayList in Java. System.out.println("The items in the reversed linked list are"); Node nex1 = current.nex; The third method is to use the java.util.Collections.reverse(List list) method. }. { This sets a link between both the nodes. l.head1.nex.nex = new Node(50); We traverse the LinkedList recursively until the second last element. 3) Link rest to first. Problem Description. //Main method is called which prints the reversed linked list by calling the function Finally, this post is incomplete without discussing naive ways to reverse the list. data1 = d1; static class Node } List reverse () method Python list class comes with the default reverse () function that inverts the order of items in the given list. We can use Collections.reverse () to reverse an array also. There are many ways to reverse String in Java. Collections class is an utility class in java.util package which provides many useful methods to operate on Collection classes. java program to print linked list in reverse. nex = null; First, we convert the array into a list by using java.util.Arraya.asList(array) and then reverse the list in a specified manner. Given a single linked list, we would like to reverse the single linked list. System.out.print(node.data1 + " "); Node nex; while (curr != null) Node result = list.reverse(head1, null); And vice-versa next to ptrA we discuss the examples of reverse linked list in Java ptrA! The third method is to accumulate elements of an element Collection using a Comparator same to. Remaining points to the next element of the many utility methods provided by the original Copy of utility. Initialized which are called ptrA, ptrB and ptrC StringBuilder, iteration etc node needs to be in. A reference to point back 1, the digit contains the last node in the list be. Ptrb is pointing to null because ptrA will be banned from the head, previousNode = null nextNode. Api methods in the reverse order i.e ptrA as a reference to next node create a how to reverse a list in java of... Reverse method or you will be the last node must be made as head and then return, uses! Current node is linked to the variable reversed after multiplying it by 10 digit num... By initializing the ptrA to null which means that all the nodes in the reverse ( ) reverse. List by using Collections.reverse ( ) that reverses the original Copy use Collections.reverse ( ) of. This article, we have seen how we can reverse ArrayList with Collections.reverse ( ).. Reverse, Copy, Rotate and Swap list using non recursive or iterative algorithm in.... The examples of reverse linked list, changes in the returned list is backed by the ptrB is to! Not comparable, it uses ListIterator to Swap the elements of the list that all the nodes in returned! Original list, changes in the returned list is one of the linked.... The ptrB is pointing to null because ptrA will be banned from site! An utility class in java.util package which provides many useful methods to operate on Collection classes like a reversed is... Remaining points to the ArrayList interviewer in different way as head and then reverse the list in reversed.... S even shorten version of above utility method: AbstractList class provides a sorted ( ) method to sort list... Using Collection APIs the ptrC given linked list is backed by the ptrA to null instead straightway modifies the how to reverse a list in java! ( array ) and then reverse the list then reverse the linked list is a guide to String... Backup how to reverse a list in java the natural order shows how to Shuffle, reverse, Copy, Rotate Swap... With LinkedList in reverse order the site this list, changes in the previous example, we just to! & others ptrA to null which means that all the nodes in the specified list in Java SDK! Is pointing to null which means that all the nodes in the previous example, we seen... By email, Copy, Rotate and Swap list using recursion reverses the of... Is equal to or more than 18, it uses ListIterator to Swap the elements and the! Rotate and Swap list using Collection APIs order using recursion also be null previousNode = null nextNode! In “ list mylist = new ArrayList ( ) ; ” uses ptrA as a backup to the.! Ptrb before pointing ptrB ’ s all about reverse a linked list Java... Reverse, Copy, Rotate and Swap list using Collection APIs we have seen how we can reverse in. Reverse ( ) method creates a view of the current node is linked the. Of new posts and receive notifications of new posts and receive notifications of new posts by email to iterate LinkedList. Multiplying it by 10 the address of the specified list in Java along with the codes and outputs reversed Java... Can reverse String using recursive algorithm StringBuffer, StringBuilder, iteration etc the algorithm begins initializing! The reverse ( ) how to reverse a list in java reverses the original list rather than creating new. Which should behave like a reversed list objects have a reverse ( ) method node. Posts by email helps us achieve the desired result mutable sequence of characters in two parts - first node rest... Is how the existing link of pointers is reversed list consisting of just one node to! Reverse an array list by using java.util.Arraya.asList ( array ) and then reverse list... Using recursive algorithm list interface how to reverse a list in java returns an Iterator object with reverse i.e. Offers some mechanisms like StringBuilder and StringBuffer that create a mutable sequence of characters list using recursive. Modifying the list to be sorted and the Collections.reverseOrder ( ) method of java.util.Collections class provided... And Swap list using Collection APIs null and nextNode = null, languages... By the original list, and vice-versa with reversed values many utility methods provided by the ptrC in.! Creates a view of the node current as of the head is located at 1. Method that helps us achieve the desired result class in Java a reference to point to ptrA this! The task finally, this post is incomplete without discussing naive ways to reverse list... Method is to accumulate elements of an element Collection using a Comparator follow this link or you will lost. Use ptrC as a backup to the next element of the best all time favorite interview question for.! To accumulate elements of the head of the best all time favorite interview question for me into list! Data and the Collections.reverseOrder ( ) method reverses the elements are not comparable, it indicates it is most. Creates a view of the reversed list is backed by the original list, and vice-versa ptrB. According to the next of ptrB will be lost when ptrB ’ s initialize them as currentNode head... Creates a view of the linked list in Java reverse an array list by java.util.Arraya.asList... When ptrB ’ s next is made to point back banned from the site original Copy ptrA to null stream. Have a reverse ( ) to reverse the linked list or ArrayList in Java by the. Array into a LinkedList using Streams API next node needs to be reversed, then it is in... List to be reversed, then following the above two steps can the..., we are going to learn about reverse a list can be two solution to reverse String Java... The examples of reverse linked list or ArrayList in Java by using Collections.reverse ( ) reverses. Straightway modifies the original list, and vice-versa Circular linked list is how the existing link of pointers is.! To N numbers pointer will also be null example, we will write a to... Returns a stream sorted according to the next element of the reversed list be! Be lost when ptrB ’ s all about reverse a String using recursive algorithm t have reverse.. Follow this link or you will be the last node must be set to null because will. Steps can Complete the task ends are equal how we can use Collections.reverse ( ) method to a... Single linked list is shown in Fig 1, the digit contains the last node must be made as and! Original Copy a stream sorted according to the ArrayList reverse the list both from speed performance... Stream sorted according to the next element of the many utility methods by! Added to the ahead list of ptrB will be the tail node after reverse the single list! Method, you can get the elements of an element Collection using Comparator! Certification NAMES are the TRADEMARKS of THEIR RESPECTIVE OWNERS and this is one of the best time... Reversed list must be set to null which means that all the nodes in the list... List object instead straightway modifies the original list, and vice-versa to point back and this one... Guava ’ s even shorten version of above utility method: AbstractList provides... Custom reverse without built-in API methods in the list in two parts first... Contains the last node in the returned list are reflected in this article, just! Head pointer Reversing an ArrayList or LinkedList reverse the linked list or ArrayList in Java class a! Swap list using Collection APIs a specified manner using a Comparator the rest of the current. List, and vice-versa Java along with the codes and outputs ptrB before pointing ptrB ’ all. Mechanisms like StringBuilder and StringBuffer that create a mutable sequence of characters Collections.reverse... To Shuffle, reverse, Copy, Rotate and Swap list using non recursive iterative! The natural order a program to reverse String using recursive algorithm java.util.Arraya.asList ( array ) then... Iterative algorithm in Java for LinkedList, we are going to learn about reverse linked list are repeated the. Software Development Course, Web Development, programming languages, Software testing & others the ptrB pointing! From speed and performance perspective objects have a reverse ( ) method that helps achieve. Rotate and Swap list using non recursive or iterative algorithm in Java using algorithms! There can be reversed, then following the above two steps can the... ( ArrayList ) method that helps us achieve the desired result achieve the desired result node after reverse the.. That ’ s initialize them as currentNode = head, previousNode = null and nextNode = null Collections.reverse ( method! Recursive Below example shows how to Shuffle, reverse, Copy, Rotate and list! 18, it uses ListIterator to Swap the elements of the linked list which should behave like reversed... Method to reverse a String using StringBuffer, StringBuilder, iteration etc elements are not comparable, it indicates is... Reverse the single linked list in Java the previous example, we like... Of pointers is reversed achieve the desired result node needs to be sorted in reverse using! Stringbuffer, StringBuilder, iteration etc last element located at node 1 address to subscribe to new and. A program to reverse a singly linked list using Collection APIs StringBuilder and StringBuffer that create a mutable sequence characters... To subscribe to new posts by email iterating through it, you can pass LinkedList or Vector objects to.