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15 Linked List Interview Questions for Software Engineering Interviews

Hello guys, if you are preparing for Software Development interview or want to become a Software Engineer in 2023 then you must pay full attention to two important topics: first is Data Structure and Algorithms, and second is System Design. These two topics are very essential and you will always find questions from these in any coding interview. They are also the most difficult to crack as they are very vast, no matter how much you will prepare there will be certain questions which you don't know but if you have solid knowledge of fundamental data structure like array, linked list, binary tree, hash table, heap, and graphs as well sorting and searching algorithms like quicksort, merge sort, selection sort, insertion sort, binary tree as well advanced String and graph algorithms then you can still do well.

In the past, I have shared many questions on array, binary tree, hash table and string but not on linked list hence I am going to fill that gap today and share common linked list questions which you can practice to learn one of these important data structure in depth.

If you don't know, along with array, linked list is one of the two fundamental ways to store linear data. In array you store them together in one memory location while linked list allows you to store them on different places in memory. It offer an alternative which is quite important for large data set because you may not always a big chunk of memory to store 1 million records but you may be able to put them if you store them in different places. 

But how does it possible? How are you going to retrieve the data or search if something exists in your data store if its stored in different location inside memory? Well its possible because linked list contains nodes and each node has a data part and an address part which points to the location of next node. 

So basically you search one by one and that's why in worst case you need to search through all nodes if the data you are looking for is stored in last node. Hence, time complexity of search in linked list is O(n) where n is number of nodes. 

15 Linked List Interview Questions for Software Engineering Interviews

At the same time, adding and removing data in linked list is rather easy compared to array as you don't need to shift all the elements to keep them in contiguous memory location. All you need to do here is update a link when you add or remove elements from linked list, hence adding element to head and tail is O(1) in linked list because you store their address inside list. 

Another important quality of linked list data structure is that they are recursive in nature. What does that mean? This means if you take one node form the linked list out then remaining is still a linked list and you can still navigate it the same way you are navigating before. That's the reason you can use recursion to solve many of the linked list problems like reversing a linked list or checking if a linked list is palindrome or not

Now its time to look at common linked list questions you can practice to learn more about this data structure but before solving them, I suggest learn to impalement linked list in your favorite programming language like Java. 

While Java API has a LinkedList class you don't need it to solve linked list based problems, instead you can simply create a Node or ListNode class to start with a linked list, if you struggle, see how I implemented linked list in Java, and now its time for questions

15 linked list Interview questions for Programmers

Here is a list of common linked list questions you can solve to get a feel of this data structure:
  1. Reverse a singly linked list using recursion (solution)
  2. Merge two sorted linked lists
  3. How to remove duplicate elements from linked list in Java? (solution)
  4. Reverse a Linked List - Iterative
  5. Reverse every alternate k nodes of a Linked List
  6. How to find nth Node from the end of a Linked List (solution)
  7. How to calculate sum of Two Linked Lists using Stacks?
  8. How to perform union of two linked list in Java? (solution)
  9. LRU Cache Implementation
  10. Detect a loop in a linked list and find the node where the loop starts. (solution)
  11. Convert a sorted Doubly Linked List to Balanced Binary Search Tree
  12. Convert a binary tree to doubly linked list
  13. How to find middle element of a linked list in single pass? (solution)
  14. Sum of Two Linked Lists using Recursion | Set 1
  15. How to find length of a singly linked list? (solution)
  16. Sum of Two Linked Lists using Recursion | Set 2
  17. Find intersection of two Linked Lists
  18. Find intersection of two Linked Lists - O(m + n) Time Complexity and O(1) Space Complexity
  19. Find maximum element from each sub-array of size 'k'| Set 2

5 Things Programmer should remember about Linked List

Now let's revise the things every programmer should know and remember about linked list data structure:

1. linked list is a recursive data structure which means you can use recursion to solve linked list problems. 

2. For search, time complexity is O(n) in linked list where n is number of nodes

3. For traversing in one pass, you can use two pointer algorithms to keep reference of fast and slowing moving pointers. 

4. Linked List is idea for adding and removing data as performance is O(1) if you want to add and remove from head or tail

5. Linked List provides an alternate way to store data than array and its very space efficient. 

That's all about the common linked list problem for practice, most of the question I have already solved and you can find them on my blogs but if you struggle to any questions, just ping me and I can post a solution. Also, if you got any other interesting linked list questions then feel free to share with us in comments. 

Do remember all the tips I have shared about linked list they will help you to solve these questions, particularly recursion. One more thing, if recursion is not allowed then you can use a recursive data structure like Stack to replace the recursion and convert a recursive solution to iterative one. 

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Thanks, for reading this article so far, if you like this linked list coding problems, for interviews then please share it with your friends and colleagues. If you have any questions or feedback then please drop a note. 

P. S. - If you are new to Computer Science and DSA and looking for a free online course to level up your DSA skills then I highly recommend you to check out these free data structure and algorithms courses from Udemy and Courses. It's completely free and more than 1 million students have already joined this course. It also contains courses in different programming language like Java, Python,  C, and C++.

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