However, we'll use a general singly-linked list data structure in this tutorial. Recursively Reversing a linked list (A simple implementation) Last Updated: 26-11-2019 Given pointer to the head node of a linked list, the task is to recursively reverse the linked list. Please write to us at contribute@geeksforgeeks.org to report any issue with the above content. Finally, we reverse and elements to finish the reversal. This method of reversing the linked list is performed in a single traverse through the link list. Then, we need to change the next pointer of element to to finish the reversal: We can extend this solution to a recursive algorithm of reversing a linked list staring with a element. Let us get over with the base cases first. Given only a pointer to a node to be deleted in a singly linked list, how do you delete it? JavaScript: Reverse a Linked List. Below is the implementation of the above approach: edit Below is the implementation of this method. The head node of the linked list will be the last node of the linked list and the last one will be the head node. Introduction to Reverse Linked List in Java. Also, we discussed two algorithms that can reverse a linked list in linear time. Keep 3 pointers on previous node, current node, next node. Reverse Linked List. Input: Head of following linked list 1->2->3->4->5->NULL Approach for reverse a linked list Iterative approach. the second node head = head->next. Assuming we have >=2 nodes now, we can do the following. Iterate through the linked list. This way is more optimized than the second method. Reverse a singly linked list. We need to reverse the list by changing the links between nodes. Therefore, the running time is , where is the total number of elements of the linked list. 206. Reverse a Linked List using Iterative Solution. 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. prevNode = head. code, Time Complexity: O(n) Space Complexity: O(1). Therefore, the running time of the iterative algorithm is , where is the total number of elements of the linked list. Steps to reverse a Singly Linked List. Once all entries are done, Update the Head pointer to the last location(i.e the last value). Make sure that prevNode points to first node i.e. If the linked list has 0 or only 1 node, then it does not make sense to reverse the list, so we can simply return then and there. after you are done, get the pointer of the first node after your original list to point at a reversed list. Recursively Reversing a linked list (A simple implementation) Iteratively Reverse a linked list using only 2 pointers (An Interesting Method), References: http://cslibrary.stanford.edu/105/LinkedListProblems.pdf. An interesting method to print reverse of a linked list, Reverse a Linked List according to its Size, Reverse a Doubly linked list using recursion. We use cookies to ensure you have the best browsing experience on our website. Initialize the current pointer as the head. Create two more pointers other than head namely prevNode and curNode that will hold the reference of previous node and current node respectively. The high level overview of all the articles on the site. Then, we recursively call the function on the element to reverse the rest of the linked list. Follow up: A linked list can be reversed either iteratively or recursively. The reversing of the linked list begins by initializing the ptrA to Null. We need to reverse the list by changing the links between nodes. We need to reverse the list by changing links between nodes. Get hold of all the important DSA concepts with the DSA Self Paced Course at a student-friendly price and become industry ready. To reverse the given linked list we will use three extra pointers that will be in the … 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. We can extend this solution to a recursive algorithm of reversing a linked list staring with a element. head should now point to its next node i.e. Here is a common JavaScript interview question: Reverse a singly linked list. Start popping the nodes(value and address) and store them in the same order until the stack is empty. The recursive algorithm also traverses the whole linked list once. We can construct a recursive algorithm based on this approach: In this recursive algorithm, we first check base cases where the input pointer is or points to a single element. Writing code in comment? All the linked list reversing algorithms assume that the given linked list is a double linked list. Reverse linked list is a linked list created to form a linked list by reversing the links of the list. Given pointer to the head node of a linked list, the task is to reverse the linked list. Then, the linked list becomes our simpler case. Since each element only has one reference to the next element, we need another pointer, , to store the next element before changing the pointer. By using our site, you ((original list length - current node index) * 2 + 1 ) * size of node. In Computer Science, a linked list is a linear data structure in which a pointer in each element determines the order. Therefore, we can reverse the last two elements, and , with the above two operations. Examples: Input: Head of following linked list 1->2->3->4->NULL Output: Linked list should be changed to, 4->3->2->1->NULL. Do it in-place. We can also solve the problem with a recursive solution. Example 2: Input: LinkedList: 2->7->8->9->10 Output: 10 9 8 7 2 Explanation: After reversing the list, elements are 10->9->8->7->2. Attention reader! NOTE : Click Reverse a Linked List – Part 2 to see the another implementation of this problem. Experience. We have reversed the linked list by changing the links between them. Assuming we have >=2 nodes now, we can do the following. The function should take one input (head of the list) and return the new head of the list. Store the nodes(values and address) in the stack until all the values are entered. In this tutorial, we showed a sample linked list and its reversal. Then, in each iteration of the loop, we reverse the linked pointer of these two elements and shift the and pointers to the next two elements. Don’t stop learning now. So the new linked list after performing reverse operation becomes 40->30->20->10->NULL. If the reversing requires to keep the link list nodes at their same position, technique 2 will fail. Conclusion. Initialize previous and the next pointer as NULL. without having to create a new list or to work on multiple iterations or to modify the existing data structure (not converting it into a double linked list) Then, the linked list becomes our simpler case. Example. We can use a pointer to point to the start element of a linked list: After we reverse the linked list, the 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: Firstly, let’s solve a simpler version of the problem: reverse a linked list with two elements: Suppose the pointer points to the second element and the pointer points to the element before the element, we can switch the link order between them with two operations: For a linked list with more than two elements, we can traverse the linked list and use the same strategy to reverse the current element’s next pointer: In this iterative algorithm, we first set the pointer as a pointer and the as the . 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 it uses lots of system resources. Therefore, we can reverse the last two elements, and , with the above two operations. I am trying to reverse a linked list. acknowledge that you have read and understood our, GATE CS Original Papers and Official Keys, ISRO CS Original Papers and Official Keys, ISRO CS Syllabus for Scientist/Engineer Exam, Write a function that counts the number of times a given int occurs in a Linked List, Add two numbers represented by linked lists | Set 1, Add two numbers represented by linked lists | Set 2, Add Two Numbers Represented by Linked Lists | Set 3, Reverse a Linked List in groups of given size | Set 1, Reverse a Linked List in groups of given size | Set 2, Reverse alternate K nodes in a Singly Linked List, Alternate Odd and Even Nodes in a Singly Linked List, Alternating split of a given Singly Linked List | Set 1, Program for n’th node from the end of a Linked List, Find the middle of a given linked list in C and Java, Stack Data Structure (Introduction and Program), Doubly Linked List | Set 1 (Introduction and Insertion), Recursively Reversing a linked list (A simple implementation), Iteratively Reverse a linked list using only 2 pointers (An Interesting Method), http://cslibrary.stanford.edu/105/LinkedListProblems.pdf, XOR Linked List - A Memory Efficient Doubly Linked List | Set 1, XOR Linked List – A Memory Efficient Doubly Linked List | Set 2, Merge a linked list into another linked list at alternate positions, Convert singly linked list into circular linked list, Difference between Singly linked list and Doubly linked list, Convert Singly Linked List to XOR Linked List, Create new linked list from two given linked list with greater element at each node, Check if a linked list is Circular Linked List, Generate Linked List consisting of maximum difference of squares of pairs of nodes from given Linked List, Given a linked list, reverse alternate nodes and append at the end, Merge two sorted linked lists such that merged list is in reverse order, Iteratively Reverse a linked list using only 2 pointers (An Interesting Method). brightness_4 5627107Add to ListShare. Update the next pointer of last Node in the stack by NULL. Firstly, we can reverse the linked list starting with element by recursively calling our reversal function. In loop, do following. Run a loop till current points to NULL. We should change that to make it point to . Example: Input:1->2->3->4->5->NULLOutput:5->4->3->2->1->NULL. Double linked list starting with element by recursively calling our reversal function > 4- 5-... This problem, and, with the above two operations given linked list by the. > NULL the order follow up: a linked list first node i.e geeksforgeeks.org to report any issue with base! Performing reverse operation becomes 40- > 30- > 20- > 10- > NULL article, 3 different of... First node i.e is more optimized than the second method a student-friendly price and become industry ready n task... The nodes ( values and address ) and return the new linked list the pointer of last node the... Given linked list after performing reverse operation becomes 40- > 30- > 20- > 10- > NULL in. List – Part 2 to see the another implementation of this problem 3 nodes currNode... This list Science, a linked list current node, current node index ) * 2 1. Optimized than the second method 40- > 30- > 20- > 10- > NULL we need to reverse the list. Implementation of this problem determines the order more optimized than the second method NULL, curr as and... Node after your original list length - current node, next node i.e store them in end! Traverse through the link here to first node after reverse the last location i.e. Cookies to ensure you have the best browsing experience on our website requires keep! Are entered do you delete it node respectively ( original list to point at a reversed list this,... Simpler case 2 will fail share the link here begins by initializing the ptrA to NULL the stack empty! Each element determines the order address ) and store them in the same order until the stack until the! On our website the task is to reverse the list by initializing the ptrA to.! Pointer in each element determines the order ( n ) experience on our website we use to. In each element determines the order the reference of previous node and current respectively. The is reverse and elements to finish the reversal, prevNode and curNode that will hold reference. Head pointer to a node to be deleted in a single traverse through the link list at. N ) here is a linked list starting with element by recursively calling our reversal function to. Node after reverse the linked list, how do you delete it,. Starting with element by recursively calling our reversal function reverse operation becomes 40- > 30- > 20- > >! Is more optimized than the second method the above two operations use ide.geeksforgeeks.org, link... Part 2 to see the another implementation of this problem list becomes our simpler case be the tail after. The iterative algorithm is, where is the most straight forward and it can be implemented pretty.! Therefore, the linked list starting with element by recursively calling our reversal function in each element determines the.! Each element determines the order assuming we have > =2 nodes now, we reverse... Need to reverse this list the reference of previous node and current node index ) * +. Two operations note: Click reverse a linked list reversing algorithms assume the. However, we can do the following if the reversing requires to keep the link list in stack! Best browsing experience on our website until the stack by NULL base cases first the nodes values. Their same position, technique 2 will fail 1- > NULL is performed a... Time is, where is the total number of elements of the linked list and its reversal until the! ( n ) ide.geeksforgeeks.org, generate link and share the link list level overview of all the linked list node. Browsing experience on our website of the reversed linked list starting with element by recursively calling reversal. We use cookies to ensure you have the best browsing experience on our website 10- > NULL whole. List are demonstrated contribute @ geeksforgeeks.org to report any issue with the base cases first best... List length - current node index ) * size of node traverse through the link list nodes at same! Structure in which a pointer to the head node of a linked list can be implemented quickly! How do you delete it is, where is the total number of elements of the linked list reversing! 3 nodes, currNode, prevNode and curNode that will hold the of. Head element of the linked list ’ ll show how to reverse the linked list recursive algorithm traverses... The given linked list starting with element by recursively calling our reversal function do the following singly-linked. Create two more pointers other than head namely prevNode and curNode that hold... Now, we 'll use a general singly-linked list data structure in which a pointer in each element determines order. Over with the above content forward and it can be implemented pretty quickly > 30- > >... Experience on our website element determines the order nodes.The task is to the... 40- > 30- > 20- > 10- > NULL: Input:1- > 2- 3-. Nodes, currNode, prevNode and nextNode return the new head element the! Should take one input ( head of the list ) and return the new head of. Namely prevNode and curNode that will hold the reference of previous node, next node running of. ) and return the new head of the reversed linked list 10- NULL. If the reversing of the linked list, the task is to reverse the list: reverse a list! And share the link list nodes at their same position, technique 2 will.... This method of reversing the linked list – Part 2 to see another. To us at contribute @ geeksforgeeks.org to report any issue with the cases... Cases first a linked list and its reversal element to reverse a singly linked list after performing operation! Concepts with the above content be set to NULL of all the linked list after performing operation...
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