How To Contrary A Linked Listing Inward Coffee Using Recursion As Well As Iteration (Loop) - Example

There are a pair of algorithms exists to contrary a singly linked listing inwards Java e.g. You tin usage the three-pointers approach or solve this occupation using a stack, or exactly using recursion without the external stack. As I had pointed out on the earlier post well-nigh linked list, that reversing a linked listing is 1 of the most pop information construction interview question, based on linked list, which means, you lot exactly can't afford to laid this one, before going for whatever programming interview. Despite beingness thence common, It's non slow to solve this occupation on the fly. Many Java programmer struggles to contrary a linked listing using both iteration too recursion, which makes this inquiry real useful for filtering programmers who tin code too who are non thence proficient amongst coding. Indeed, this is 1 of the confusing algorithms to empathise too it's non slow to grasp, particularly if you lot haven't practiced linked listing based questions e.g. finding middle node of linked list inwards 1 piece of work past times or inserting too removing an chemical constituent from linked listing information structure.

Since Java programmer gets a linked listing implementation inwards the shape of java.util.LinkedList, they never bother to do this exercise past times hand. Yes, in that place are some exceptions but many Java programmer doesn't focus plenty on information construction too manus coding, which is actually of import to improve your problem-solving skills for the interview.

So, when it comes to pattern a whole organization using Object oriented analysis too pattern e.g. implementing a vending motorcar inwards Java, sometimes they neglect to conduct the right information construction too devising unproblematic algorithms.

Before going for a programming/coding interview, It's absolutely necessary to do equally much exercise inwards information construction too algorithm equally possible to accept wages of all the noesis available. This volition improve your thinking ability, problem-solving science too you lot volition last to a greater extent than comfortable amongst dealing amongst the unknown laid of problems. This advice is irrespective of whether you lot are a Java, C++, or Python developer.

Java Program to Reverse a singly linked listing using recursion too Iteration

Influenza A virus subtype H5N1 linked listing is a information construction which contains nodes, every node cash inwards one's chips on information too pointer to adjacent node. This way linked listing grows too tin shop equally many elements equally much retentivity allows it. It's non similar an array which requires a contiguous chunk of retentivity because hither node tin last stored at whatever retentivity location.

This construction means, adding too removing elements inwards linked listing is slow but searching an chemical constituent is expensive because you lot demand to traverse entire listing to uncovering the element. It doesn't assist fifty-fifty if you lot know that chemical constituent is the fifth node or sixth node because you lot cannot access them past times index similar an array. This is the biggest difference betwixt an array too linked listing information structure. In the array, searching the index is O(1) functioning but inwards linked listing searching is O(n) operation.

Below code correspond a singly linked listing inwards Java, amongst express operations. I receive got already removed some non-relevant code for performing unlike operations on linked listing i.e. checking if linked listing is cyclic or not, inserting an chemical constituent at the middle, too removing the element. Since nosotros don't demand this code for reversing linked list, I receive got exactly deleted them for now.


This shape is similar to the SinglyLinkedList class, which nosotros receive got seen inwards how to implement linked listing inwards Java using generics (see here), amongst ii to a greater extent than methods for reversing linked listing using iteration too recursion.

The reverseRecursively() method reverse the linked listing using recursion. It uses the telephone telephone stack to shop data, too 1 time nosotros reached tail, which becomes novel caput for the reversed linked list, it starts adding nodes inwards contrary order. Look at some comments to a greater extent than or less those methods, which volition brand you lot empathise the algorithm of reversing linked listing better.

It is said that a pic is worth a K discussion too it is real truthful inwards the instance of problem-solving too agreement algorithms. Here are a diagram too flowchart to contrary a singly linked listing using recursion. It divides the listing into ii parts initiative off node too residuum of list, and too thence link residuum to caput inwards contrary order. It too thence recursively applies same segmentation until it reaches the finally node, at that betoken whole linked list, is reversed. 

The reverseIteratively() method reverses linked listing using the three-pointers approach too using loops, that's why it is called iterative solution. It traverses through the linked listing too adding nodes at the starting fourth dimension of the singly linked listing inwards each iteration. It uses iii reference variables (pointers) to cash inwards one's chips on rail of previous, current, too adjacent nodes.

If you lot are non real familiar amongst linked listing information construction or desire to larn to a greater extent than well-nigh linked listing information structure, you lot should initiative off read a proficient mass on information construction too algorithm e.g. Data Structures too Algorithms Made Easy inwards Java past times Narasimha Karumanchi, 1 of the best books to larn information construction too algorithms.

Java Class to correspond Singly Linked List

Here is our Java programme solve this problem. As I said, it contains a shape to correspond singly linked listing too it contains some other shape which has the principal method for testing. That shape creates an instance of linked listing too and thence telephone telephone relevant methods to contrary the linked listing past times using iteration too recursion. 

/**   * Java Class to correspond singly linked listing for demonstration purpose.   * In club to empathise How to contrary linked list, focus on ii methods   * reverseIteratively() too reverseRecursively().    * @author Javin Paul   */ public class SinglyLinkedList {     private Node head;  // Head is the initiative off node inwards linked list      public void append(T data){         if(head == null){             caput = new Node(data);             return;         }         tail().next = new Node(data);     }       private Node tail() {         Node tail = head;               // Find finally chemical constituent of linked listing known equally tail         while(tail.next != null){             tail = tail.next;         }               return tail;           }        @Override     public String toString(){         StringBuilder sb = new StringBuilder();         Node electrical flow = head;         while(current != null){            sb.append(current).append("-->");            electrical flow = current.next;         }             if(sb.length() >=3){             sb.delete(sb.length() - 3, sb.length()); // to withdraw --> from finally node         }               return sb.toString();     }      /**       * Reverse linked listing using 3 pointers approach inwards O(n) fourth dimension       * It basically creates a novel listing past times reversing direction, too       * after insert the chemical constituent at the start of the list.       */     public void reverseIteratively() {         Node electrical flow = head;         Node previous = null;         Node forrard = null;               // traversing linked listing until in that place is no to a greater extent than element         while(current.next != null){                       // Saving reference of adjacent node, since nosotros are changing electrical flow node             forrard = current.next;                       // Inserting node at start of novel list             current.next = previous;             previous = current;                       // Advancing to adjacent node             electrical flow = forward;         }               caput = current;         head.next = previous;     }       /*      * Reverse a singly linked listing using recursion. In recursion Stack is      * used to shop data.         * 1. Traverse linked listing till nosotros uncovering the tail,       * that would last novel caput for reversed linked list.      */     private Node reverseRecursively(Node node){        Node newHead;              //base instance - tail of master copy linked list        if((node.next == null)){            return node;        }        newHead = reverseRecursively(node.next);              //reverse the link e.g. C->D->null volition last naught               node.next.next = node;        node.next = null;            return newHead;     }        public void reverseRecursively(){         caput = reverseRecursively(head);     }        private static class Node {         private Node next;         private T data;          public Node(T data) {             this.data = data;         }          @Override         public String toString() {             return data.toString();         }     }   }

Test Class

Here is our examine class, which volition examine both methods of reversing linked list, reverseIteratively() too reverseRecursively(). We receive got initiative off created a singly linked listing amongst half dozen nodes A-B-C-D-E-F, too initiative off reversed them iteratively using 3 points approach too later reversed the same listing recursively. Since the same instance of the singly linked listing is reversed ii times, you lot tin run across inwards the output that terminal listing is same equally master copy linked list.

/**   * Java programme to examine code of reversing singly linked listing inwards Java.   * This examine shape examine both iterative too recursive solution. Since   * the same listing is initiative off reversed using loops, too and thence 1 time to a greater extent than using recursion.   * You tin run across that terminal output is same equally master copy linked list.    * @author Javin Paul   */ public class SinglyLinkedListTest {      public static void main(String args[]) {        SinglyLinkedList linkedlist = getDefaultList();        System.out.println("linked listing before reversing : " + linkedlist);             linkedlist.reverseIteratively();             System.out.println("linked listing after reversing : " + linkedlist);        linkedlist.reverseRecursively();        System.out.println("linked listing after reversing recursively: " + linkedlist);                 }         private static SinglyLinkedList getDefaultList(){         SinglyLinkedList linkedlist = new SinglyLinkedList();                linkedlist.append("A"); linkedlist.append("B"); linkedlist.append("C");         linkedlist.append("D"); linkedlist.append("E"); linkedlist.append("F");         return linkedlist;     }    }  Output: linked listing before reversing : A-->B-->C-->D-->E-->F linked listing after reversing : F-->E-->D-->C-->B-->A linked listing after reversing recursively: A-->B-->C-->D-->E-->F

That's all on how to contrary a linked listing inwards Java. We receive got seen ii approaches to contrary singly linked list, initiative off using Iterations, which involves 3 pointers or reference variable; too second, which reversed linked listing using recursion. The reason, I receive got shared both approaches because they are asked equally a follow-up question, too it's ever meliorate to know both approaches to brand a proficient impression. By the way, if you lot tin improve the algorithm, too tin uncovering few to a greater extent than ways to contrary linked list, volition ever deed equally summation betoken for you. You tin equally good cheque out Cracking the code interview sixth Edition for to a greater extent than exercise questions. It contains 189 coding interview questions based upon information structure, algorithms, too other topics.

Related linked listing too information construction questions you lot may similar to explore

• When to usage ArrayList vs LinkedList inwards Java? (answer)
• How to convert linked listing to an array inwards Java? (example)
• How to uncovering the initiative off too finally chemical constituent of linked listing inwards Java? (solution)
• How to search chemical constituent within linked listing inwards Java? (solution)
• What is the deviation betwixt LinkedList too ArrayList inwards Java? (answer)
• How to contrary an array inwards house inwards Java? (solution)
• Top xxx Array-based Interview Questions for Programmers (list)
• Top v Books to Learn Data Structure too Algorithms (books)
• Top v Books for Programming too Coding Interviews (books)

Further Learning
Data Structures too Algorithms: Deep Dive Using Java
Algorithms too Data Structures - Part 1 too 2
Data Structures inwards Java ix past times Heinz Kabutz

Thanks for reading this interview question. If you lot similar this article too thence delight part amongst your friends too colleagues. If you lot receive got whatever suggestions or feedback too thence delight part your comment.

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