Reversing a linked list in java

Find the middle of a given linked list
Write a function that counts the number of times a given int occurs in a Linked List
Check if a linked list is Circular Linked List
Count nodes in Circular linked list
Convert singly linked list into circular linked list
Exchange first and last nodes in Circular Linked List
Program to find size of Doubly Linked List
An interesting method to print reverse of a linked list
Can we reverse a linked list in less than O(n)?
Traversal of Circular Linked List
Delete a node in a Doubly Linked List
Reverse a Doubly Linked List

Detect loop or cycle in a linked list
Find length of loop/cycle in given Linked List
Remove duplicates from a sorted linked list
Intersection of two Sorted Linked Lists
QuickSort on Singly Linked List
Split a Circular Linked List into two halves
Deletion from a Circular Linked List
Merge Sort for Doubly Linked List
Find pairs with given sum in doubly linked list
Insert value in sorted way in a sorted doubly linked list
Remove duplicates from an unsorted doubly linked list
Rotate Doubly linked list by N nodes
Given only a pointer/reference to a node to be deleted in a singly linked list, how do you delete it?
Modify contents of Linked List

Write a function to get the intersection point of two Linked Lists
Circular Linked List Implementation of Circular Queue
Josephus Circle implementation using STL list
The Great Tree-List Recursion Problem.
Clone a Linked List with next and Random Pointer
Convert given Binary Tree to Doubly Linked List in Linear time
Priority Queue using Doubly Linked List
Reverse a doubly linked list in groups of given size
Linked List representation of Disjoint Set Data Structures
Sublist Search (Search a linked list in another list)
Construct a linked list from 2D matrix
Partitioning a linked list around a given value and If we don’t care about making the elements of the list “stable”

Find the middle of a given linked list
Write a function that counts the number of times a given int occurs in a Linked List
Check if a linked list is Circular Linked List
Count nodes in Circular linked list
Convert singly linked list into circular linked list
Exchange first and last nodes in Circular Linked List
Program to find size of Doubly Linked List
An interesting method to print reverse of a linked list
Can we reverse a linked list in less than O(n)?
Traversal of Circular Linked List
Delete a node in a Doubly Linked List
Reverse a Doubly Linked List

Detect loop or cycle in a linked list
Find length of loop/cycle in given Linked List
Remove duplicates from a sorted linked list
Intersection of two Sorted Linked Lists
QuickSort on Singly Linked List
Split a Circular Linked List into two halves
Deletion from a Circular Linked List
Merge Sort for Doubly Linked List
Find pairs with given sum in doubly linked list
Insert value in sorted way in a sorted doubly linked list
Remove duplicates from an unsorted doubly linked list
Rotate Doubly linked list by N nodes
Given only a pointer/reference to a node to be deleted in a singly linked list, how do you delete it?
Modify contents of Linked List

Write a function to get the intersection point of two Linked Lists
Circular Linked List Implementation of Circular Queue
Josephus Circle implementation using STL list
The Great Tree-List Recursion Problem.
Clone a Linked List with next and Random Pointer
Convert given Binary Tree to Doubly Linked List in Linear time
Priority Queue using Doubly Linked List
Reverse a doubly linked list in groups of given size
Linked List representation of Disjoint Set Data Structures
Sublist Search (Search a linked list in another list)
Construct a linked list from 2D matrix
Partitioning a linked list around a given value and If we don’t care about making the elements of the list “stable”

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Reversing a Linked List in Java

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We’re looking for a new Java technical editor to help review new articles for the site.

1. Introduction

In this tutorial, we’ll implement two linked list reversal algorithms in Java.

2. Linked List Data Structure

A linked list is a linear data structure in which a pointer in each element determines the order. Each element of a linked list contains a data field to store the list data and a pointer field to point to the next element in the sequence. Also, we can use a head pointer to point to the start element of a linked list:

After we reverse the linked list, the head will point to the last element of the original linked list, and the pointer of each element will point to the previous element of the original linked list:

In Java, we have a LinkedList class to provide a doubly-linked list implementation of the List and Deque interfaces. However, we’ll use a general singly-linked list data structure in this tutorial.

Let’s first start with a ListNode class to represent an element of a linked list:

public class ListNode < private int data; private ListNode next; ListNode(int data) < this.data = data; this.next = null; >// standard getters and setters >

The ListNode class has two fields:

An integer value to represent the data of the element
A pointer/reference to the next element

A linked list may contain multiple ListNode objects. For example, we can construct the above sample linked list with a loop:

ListNode constructLinkedList() < ListNode head = null; ListNode tail = null; for (int i = 1; i else < tail.setNext(node); >tail = node; > return head; >

3. Iterative Algorithm Implementation

Let’s implement the iterative algorithm in Java:

ListNode reverseList(ListNode head) < ListNode previous = null; ListNode current = head; while (current != null) < ListNode nextElement = current.getNext(); current.setNext(previous); previous = current; current = nextElement; >return previous; >

In this iterative algorithm, we use two ListNode variables, previous and current, to represent two adjacent elements in the linked list. For each iteration, we reverse these two elements and then shift to the next two elements.

In the end, the current pointer will be null, and the previous pointer will be the last element of the old linked list. Therefore, previous is also the new head pointer of the reversed linked list, and we return it from the method.

We can verify this iterative implementation with a simple unit test:

@Test void givenLinkedList_whenIterativeReverse_thenOutputCorrectResult() < ListNode head = constructLinkedList(); ListNode node = head; for (int i = 1; i LinkedListReversal reversal = new LinkedListReversal(); node = reversal.reverseList(head); for (int i = 5; i >= 1; i--) < assertNotNull(node); assertEquals(i, node.getData()); node = node.getNext(); >>

In this unit test, we first construct a sample linked list with five nodes. Also, we verify that each node in the linked list contains the correct data value. Then, we call the iterative function to reverse the linked list. Finally, we check the reversed linked list to make sure the data are reversed as expected.

4. Recursive Algorithm Implementation

Now, let’s implement the recursive algorithm in Java:

ListNode reverseListRecursive(ListNode head) < if (head == null) < return null; >if (head.getNext() == null) < return head; >ListNode node = reverseListRecursive(head.getNext()); head.getNext().setNext(head); head.setNext(null); return node; >

In the reverseListRecursive function, we recursively visit each element in the linked list until we reach the last one. This last element will become the new head of the reversed linked list. Also, we append the visited element to the end of the partially reversed linked list.

Similarly, we can verify this recursive implementation with a simple unit test:

@Test void givenLinkedList_whenRecursiveReverse_thenOutputCorrectResult() < ListNode head = constructLinkedList(); ListNode node = head; for (int i = 1; i LinkedListReversal reversal = new LinkedListReversal(); node = reversal.reverseListRecursive(head); for (int i = 5; i >= 1; i--) < assertNotNull(node); assertEquals(i, node.getData()); node = node.getNext(); >>

5. Conclusion

In this tutorial, we implemented two algorithms to reverse a linked list. As always, the source code for the article is available over on GitHub.

Slow MySQL query performance is all too common. Of course it is. A good way to go is, naturally, a dedicated profiler that actually understands the ins and outs of MySQL.

Critically, it has very minimal impact on your server’s performance, with most of the profiling work done separately — so it needs no server changes, agents or separate services.

Basically, you install the desktop application, connect to your MySQL server, hit the record button, and you’ll have results within minutes:

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Reverse a LinkedList in Java

Assuming you have gone through LinkedList in java and know about linked list. This post contains different examples for reversing a linked list which are given below: 1. By writing our own function(Using additional space): reverseLinkedList() method contains logic for reversing string objects in a linked list. This method takes a linked list as a parameter, traverses all the elements in reverse order and adds it to the newly created linked list. Algorithm: Step 1. Create a linked list with n elements Step 2. Create an empty linked list which will be used to store reversed elements Step 3. Start traversing the list from ‘n’ to ‘0’ and store the elements in the newly created list. Step 4. The elements will be stored in the following order: n, n-1, n-2, ……0 Step 5. Return the list to the caller and print it

Example: Step 1: LL: 1 -> 2 -> 3 -> 4 -> 5 where 'LL' is the linked list with n elements Step 2: 'Rev' is an empty linked list Step 3: Start traversing, the below passes are the intermediate steps while traversing 1st pass: Rev: 5 2nd pass: Rev: 5 -> 4 3rd pass: Rev: 5 -> 4 -> 3 4th pass: Rev: 5 -> 4 -> 3 -> 2 5th pass: Rev: 5 -> 4 -> 3 -> 2 -> 1 Step 4: nth element of 'LL' is stored in 0th position of 'Rev', n-1 element of LL is stored in 1st position of Rev and so on. Step 5: Return Rev: 5 -> 4 -> 3 -> 2 -> 1 to the calling function.

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