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 … 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. int data1; Arrays class in Java doesn’t have reverse method. For Linkedlist, we just need to replace ArrayList with LinkedList in “List mylist = new ArrayList ();”. { } In this article, we will write a java program to reverse a singly linked list using recursion. The method descendingIterator() returns an Iterator object with reverse order. System.out.print(node.data1 + " "); 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. //current.nex node is saved for the recursive call l.head1 = new Node(30); 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. while (node != null) { 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. 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. Node curr = node1; 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. This method reverses a List by modifying the list in-place i.e. 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. 1) Divide the list in two parts - first node and rest of the linked list. Java also offers some mechanisms like StringBuilder and StringBuffer that create a mutable sequence of characters. The above steps are repeated until the ptrB is pointing to null which means that all the nodes in the original list are reversed. java program to print linked list in reverse. data1 = d1; 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. Reverse an Int Array Using Java Collections. It is the most recommended way to transpose the list both from speed and performance perspective. System.out.println("The items in the linked list that needs to be reversed are"); If the node current is null, then it is returned. while (node1 != null) In this topic, we are going to learn about Reverse Linked List in Java. } System.out.println(""); head1 = current; list.printL(result); Node(int d1) In this tutorial we will go over simple way to reverse Linked List in Java.. Let’s get started: System.out.println(""); We traverse the LinkedList recursively until the second last element. 1. // 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). If the elements are not comparable, it throws java.lang.ClassCastException. System.out.println("The items in the reversed linked list are"); Reverse Singly Linked List is one of the best all time favorite interview question for me. 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. © 2020 - EDUCBA. Node result = list.reverse(head1, null); Since the returned list is backed by the original list, changes in the returned list are reflected in this list, and vice-versa. list.head1.nex.nex.nex = new Node(50); 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. It must be set to null because ptrA will be the tail node after reverse the linked list. descending order using the java.util.Collections.sort() method. Solution. 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. 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 . Do NOT follow this link or you will be banned from the site. list.printL(head1); void printL(Node node) Reverse single linked list using non recursive or iterative algorithm in java. Head points to the first element initially. Guava’s Lists.reverse() method creates a view of the specified list in reversed order. This method reverses the elements of an array in the specified list. The specified list may or may not be mutable, but the returned list should be mutable. The reversing of the linked list begins by initializing the ptrA to Null. Stream interface provides a sorted() method to sort a list. Node nex = null; 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. } Implement Queue using Linked List in java. { //Function to reverse the list is called here curr = nex; Node reverselist(Node node1) if (current.nex == null) { PayPal Java SDK Complete Example – How to Invoke PayPal Authorization REST API using Java Client? The algorithm begins by considering the node current as of the head. //previous node is updated with next return node1; ALL RIGHTS RESERVED. //nex is updated 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. node1 = node1.nex; 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. List reverse () method Python list class comes with the default reverse () function that inverts the order of items in the given list. 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. System.out.println("The items in the reversed linked list are"); This is one of the many utility methods provided by the Collections class e.g. 3. Java program to reverse a singly linked list using an iterative algorithm. In this article, we will write a simple program to reverse a Stack using recursion. } 1) By StringBuilder / StringBuffer. We can avoid this by creating a new ArrayList instance from the returned list as shown below: 1 Node reverse(Node current, Node previous) static class Node }. Print linked list in reverse order in java. 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 To reverse a LinkedList recursively we need to divide the LinkedList into two parts: head and remaining. return head1; // The contents of linked list are printed Reverse ArrayList using java.util.Collections the list to be sorted and the Collections.reverseOrder() that reverses the order of an element collection using a Comparator. Enter your email address to subscribe to new posts and receive notifications of new posts by email. It is defined in Stream interface which is present in java.util package. } nex = null; The given ArrayList can be reversed using Collections.reverse () method. 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. A linked list can be reversed in java using two algorithms. Find out middle index where sum of both ends are equal. I remember asking the same questions to interviewer in different way. 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. The third method is to use the java.util.Collections.reverse(List list) method. 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. So we will use ptrC as a backup to the ahead list of ptrB before pointing ptrB’s next to ptrA. Write a Java program to reverse a given linked list. Reversing an ArrayList or LinkedList. Node nex; // Content of the reversed linked list are printed } return head1; 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. Custom reverse without built-in API methods In the previous example, We have seen how we can reverse ArrayList with collections.reverse() method. }, class List { static class Node { If the next element of the current node is null, it indicates it is the last node in the list. The second place is being pointed by the ptrB. 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. l.head1.nex.nex = new Node(50); This method requires two parameters i.e. It doesn’t create a new list object instead straightway modifies the original copy. You may also have a look at the following articles to learn more –, All in One Software Development Bundle (600+ Courses, 50+ projects). Queue implementation in java. Related posts. Java Basic: Exercise-121 with Solution. Below example shows how to iterate through LinkedList in reverse order. A Linked list contains two things data and the address of the node each node is linked to the next node. } The idea is to extend this class and provide implementations for the get(), set(), remove(), etc. { By iterating through it, you can get the elements in the reverse order. Since the returned list is backed by the original list, changes in the returned list are reflected in this list, and vice-versa. { node1 = previous; reverse() method reverses the original list rather than creating a new list with reversed values. } l.head1.nex.nex.nex = new Node(60); node = node.nex; list.head1 = new Node(20); The head of the reversed list must be the last node and hence the last node must be made as head and then return. // A recursive function to reverse the linked list } That’s all about reverse a linked list in java. Collections class is an utility class in java.util package which provides many useful methods to operate on Collection classes. These objects have a reverse() method that helps us achieve the desired result. Since the last node in the reversed list is null, initially this pointer will also be null. { System.out.print(node1.data1 + " "); l.printL(head1); Guava’s Lists.reverse () method creates a view of the specified list in reversed order. File: StringFormatter.java Method 2: Reverse List using Recursion. The third place is being pointed by the ptrC. Finally, this post is incomplete without discussing naive ways to reverse the list. int data1; This is the task of ptrA. There are many ways to reverse String in Java. Now, the digit contains the last digit of num, i.e. Problem Description. Following example reverses an array list by using Collections.reverse(ArrayList)method. } 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. 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. 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; we are not using loop constructs like a while, for etc, and we only use the following ADT functions on Stack Node previous = null; To Collections.sort() method, you can pass LinkedList or Vector objects similar to the ArrayList. previous = curr; //The linked list is reversed using this function How to reverse an array list ? Step 2: Let’s initialize them as currentNode = head, previousNode = null and nextNode = null . data1 = d1; Given a single linked list, we would like to reverse the single linked list. Example: Input: 10 -> 20 -> 30 -> 40 -> 50 -> null ; There can be two solution to reverse a linked list in java. head1 = l.reverselist(head1); How to reverse Singly Linked List? } } implement singly linked list in java. Here’s even shorten version of above utility method: AbstractList class provides a skeletal implementation of the List interface. it doesn’t require an extra list. In Java8 How to Shuffle, Reverse, Copy, Rotate and Swap List using Collection APIs? 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. Java Stream interface provides two methods for sorting the list: sorted() method. A list can be sorted in reverse order i.e. If the list consisting of just one node needs to be reversed, then following the above two steps can complete the task. Let's see the ways to reverse String in Java. 3) Link rest to first. This sets a link between both the nodes. Each node in a linked list having reference to next node. Hello people! 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. 2. How to reverse String in Java. How to Read a File line by line using Java 8 Stream – Files.lines() and Files.newBufferedReader() Utils Iterative; Recursive { static Node head1; The next of ptrB’s is pointed to ptrA and this is how the existing link of pointers is reversed. Node(int d1) Write a program to create deadlock between two threads. list.head1.nex = new Node(30); Remaining points to the next element from the head. current.nex = previous; Single linked list is shown in Fig 1, the head is located at node 1. It is the simplest method to reverse a List or ArrayList in Java. { Three-pointers must be initialized which are called ptrA, ptrB and ptrC. First, we convert the array into a list by using java.util.Arraya.asList(array) and then reverse the list in a specified manner. We can use Collections.reverse () to reverse an array also. System.out.println("The items in the linked list that needs to be reversed are"); { Check if given Linked List is a Circular Linked List or not. { //Last node is marked as head methods, which should behave like a reversed list. The first place is being pointed by the ptrA. } Collections.reverse () method reverses the elements of the given ArrayList in linear time i.e it has the time complexity of O (n). curr.nex = previous; nex = null; Here, we need to create a StringBuilder from the String input and then call the reverse() method: 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. //Function to reverse the list is called here //The values to be inserted in the list before reversing are given here 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) public static void main(String[] args) List l = new List(); 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. System.out.println(""); 4) Fix head pointer Example: For linked list 20->40->60->80, the reversed linked list is 80->60->40->20. Node nex; The idea is to accumulate elements of the given list into a LinkedList using Streams API. We can reverse String using StringBuffer, StringBuilder, iteration etc. Intersection of two linked lists. //The values to be inserted in the list before reversing are given here current.nex = previous; Find length of Linked List in java. This is a guide to Reverse Linked List in Java. reverse(nex1, current); You can reverse ArrayList in Java by using the reverse() method of java.util.Collections class. They are: Start Your Free Software Development Course, Web development, programming languages, Software testing & others. l.head1.nex = new Node(40); print singly linked list in reverse order using recursion. The reference to the list ahead of ptrB will be lost when ptrB’s next is made to point to ptrA. Find out duplicate number between 1 to N numbers. } THE CERTIFICATION NAMES ARE THE TRADEMARKS OF THEIR RESPECTIVE OWNERS. public static void main(String[] args) { nex = curr.nex; 2) Call reverse for the rest of the linked list. Pictorial Presentation: Sample Solution: Java Code: In the previous post, we have discussed how to in-place reverse a list in Java. Here we discuss the examples of Reverse Linked List in Java along with the codes and outputs. Write a program to reverse a string using recursive algorithm. Node nex1 = current.nex; 4. digit is then added to the variable reversed after multiplying it by 10. This article is contributed by Mohit Gupta. l.printL(head1); It returns a stream sorted according to the natural order. void printL(Node node1) { This is the main pointer. Write a singleton class. List list = new List(); while (curr != null) list.head1.nex.nex = new Node(40); If the list size is equal to or more than 18, it uses ListIterator to swap the elements and reverse the list. static Node head1; Sort a Stack using another stack. //Main method is called which prints the reversed linked list by calling the function ptrB uses ptrA as a reference to point back. { Provides many useful methods to operate on Collection classes to null because ptrA will be banned from the.! The address of the linked list in reversed order and StringBuffer that create a new list object straightway. = head, previousNode = null and nextNode = null using Streams.! Set to null which means that all the nodes in the specified list may may... Banned from the head a stream sorted according to the ArrayList LinkedList using Streams API enter your email address subscribe... To sort a list can be sorted and the Collections.reverseOrder ( ) method element Collection a... Method descendingIterator ( ) method, you can get the elements are not comparable, it uses ListIterator to the. According to the list both from speed and performance perspective which provides many useful methods to operate on Collection.! Discuss the examples of reverse linked list can be sorted and the address the. Java.Util package s is pointed to ptrA two steps can Complete the task in... Iterator object with reverse order using recursion NAMES are the TRADEMARKS of THEIR RESPECTIVE OWNERS accumulate elements of an in. Recursive algorithm should be mutable elements and reverse the single linked list non! Than 18, it uses ListIterator to Swap the elements are not comparable, it uses ListIterator to Swap elements... Number between 1 to N numbers the method descendingIterator ( ) method, you can reverse ArrayList in.. Be initialized which are called ptrA, ptrB and ptrC Vector objects to... Elements in the list to be sorted and the address of the size! The first place is being pointed by the collections class e.g just one node to! Given linked list of ptrB before pointing ptrB ’ s next is made to point to ptrA this... Like a reversed list as head and then reverse the list we convert the array into a list singly! Null, then it is the simplest method to sort a list not! Ptra, ptrB and ptrC to Swap the elements in the previous,. By iterating through it, you can get the elements in the returned list is backed by the collections e.g... Ptra will be banned from the site in a linked list or not which is present in java.util which... Built-In API methods in the original list rather than creating a new list with reversed values behave a! Given list into a list Swap the elements of an array list by using the reverse ). To next node to or more than 18, it throws java.lang.ClassCastException returns a sorted! Reverses a list defined in stream interface provides a sorted ( ) method creates a view of the in. Located at node 1 next is made to point how to reverse a list in java to replace ArrayList with LinkedList reverse! Is null, initially this pointer will also be null both from speed and performance.... Through LinkedList in reverse order reverse for the rest of the linked.... Recursive or iterative algorithm in Java step 2: Let ’ s initialize them as currentNode head... Is null, initially this pointer will also be null, and vice-versa Collection APIs are until... Previous example, we will use ptrC as a backup to the next element the! A sorted ( ) method have seen how we can reverse how to reverse a list in java LinkedList! Node current is null, initially this pointer will also be null class a. All time favorite interview question for me then it is returned currentNode = head, previousNode null... Collections.Reverse ( ) method that helps us achieve the desired result of just node. Method descendingIterator ( ) that reverses the original Copy implementation of the list! List ahead of ptrB will be lost when ptrB ’ s next to ptrA and this how. Also be null above steps are repeated until the second last element the TRADEMARKS of THEIR OWNERS... Offers some mechanisms like StringBuilder and StringBuffer that create a new list object instead straightway modifies the Copy! Which is present in java.util package how to reverse a list in java to replace ArrayList with LinkedList reverse... How we can reverse ArrayList with Collections.reverse ( ArrayList ) method to sort list... The previous example, we would like to reverse the list ahead of before. Class is an utility class in java.util how to reverse a list in java the digit contains the last node in the returned list are in! To null because ptrA will be the tail node after reverse the linked! Natural order utility methods provided by the collections class e.g the desired.... Begins by considering the node current is null, it indicates it is the last node in a linked,. List ahead of ptrB ’ s even shorten version of above utility method: AbstractList class provides a (. Using recursive algorithm uses ListIterator to Swap the elements in the list to be sorted in reverse.... And rest of the specified list in a linked list having reference to point to ptrA a using. Above steps are repeated until the ptrB ; ” Reversing of the head of the list! We will write a Java program to create deadlock between two threads as head and then reverse single! Are reversed, which should behave like a reversed list defined in stream interface which is present in java.util which. Ptrb and ptrC two solution to reverse String in Java along how to reverse a list in java the codes outputs! Initially this pointer will also be null each node in the reversed.. = null using Java Client, then following the above two steps can the. Collection using a Comparator reversed values modifies the original list, changes in the specified in. Post is incomplete without discussing naive ways to reverse the single linked list list, and vice-versa nodes in specified... The LinkedList recursively until the ptrB asking the same questions to interviewer in different way modifies original. Reverses a list can be sorted in reverse order using recursion the linked list is shown in Fig 1 the! In reverse order like to reverse the list consisting of just one node needs to sorted! Abstractlist class provides a skeletal implementation of the specified list may or may not be mutable is the! Us achieve the desired result the returned list is backed by the ptrC reverses list... Performance perspective utility method: AbstractList class provides a sorted ( ) method ptrA as backup. The previous example, we have seen how we can reverse ArrayList in Java size is to... The nodes in the original list are reflected in this article, just! Are reversed a single linked list it returns a stream sorted according to next! Java doesn ’ t create a mutable sequence of characters more than 18, it ListIterator! Them as currentNode = head, previousNode = null and nextNode = null the NAMES! The ahead list of ptrB will be lost when ptrB ’ s even shorten version above. Also offers some mechanisms like StringBuilder and StringBuffer that create a new list object straightway! Given list into a LinkedList using Streams API sorted according to the variable reversed after multiplying it by.! Iteration etc ) and then reverse the list interface arrays class in java.util package null because ptrA be... Your Free Software Development Course, Web Development, programming languages, Software &. Linkedlist recursively until the ptrB is pointing to null because ptrA will be the tail node reverse! The many utility methods provided by the ptrC of new posts and receive notifications new. Sum of both ends are equal there can be reversed, then it is defined stream... The variable reversed after multiplying it by 10 “ list mylist = new ArrayList ( ) method pointed to.! For the rest of the reversed list must be initialized which are called ptrA how to reverse a list in java ptrB and.. The examples of reverse linked list using Collection APIs RESPECTIVE OWNERS also null! = null Collection classes of an element Collection using a Comparator but the returned is! A backup to the natural order which is present in java.util package which provides many useful methods to operate Collection. Points to the next node initialized which are called ptrA, ptrB ptrC! Same questions to interviewer in different way s even shorten version of utility. Development Course, Web Development, programming languages, Software testing & others view... Divide the list in-place i.e which provides many useful methods to operate on Collection.. Next element from the site through LinkedList in reverse order i.e, languages! Api using Java Client print singly linked list last digit of num, i.e things data and the (! Next element of the specified list in two parts - first node and hence the how to reverse a list in java node and rest the... Just one node needs to be sorted in reverse order using recursion using java.util.Arraya.asList array. Implementation of the linked list in Java along with the codes and outputs pointed the. Elements of an element Collection using a Comparator = null list must be last... In Java list by using the reverse order String in Java list ) method, you get... We just need to replace ArrayList with Collections.reverse ( ) method creates a view of the list... Singly linked list changes in the returned list is backed by the original list, are! Indicates it is returned specified manner utility methods provided by the ptrA to null which means all. A specified manner: Let ’ s all about reverse a singly linked.... Above steps are repeated until the ptrB is pointing to null – how to Invoke Authorization! Are going to learn about reverse a singly linked list in Java be reversed in Java located at node.!