15 LeetCode problems to get better at Linked List
Solve these Leetcode problems to get better at Linked List for coding interviews
Preparing for technical interviews can be a daunting task, especially when it comes to linked lists. They are tricky to solve on coding interviews and you must prepare them in advance.
If you are looking for linked list problems or coding interview resources then you have come to the right place. In the past, I have shared best coding interview books, courses, websites, and 100+ coding problems and today, I am going to share 20 Leetcode problems you can solve to get better at linked list, both singly and doubly linked list.
To help you ace your next interview, I’ve compiled a list of common linked list problems along with brief descriptions, hints for solving them, and links to detailed solutions.
These questions cover a range of topics, from basic operations to more complex challenges, ensuring you’re well-prepared for any linked list-related questions that come your way.
Though, if you are serious about cracking coding interview I also suggest you to read books like Cracking the Coding Interview by Gayle Laakmann McDowell, and Programming interview exposed, they are not the most interactive or comprehensive resources but I have used them a lot.
Since with time, interviews are also changing you need to keep yourself updated with the latest programming job interviews and coding problems.
Alternatively, you can also explore online courses like Master the Coding Interview: Big Tech (FAANG) Interviews by Andrei Negaoie on Udemy to properly prepare for coding Interviews.
They cover topics like data structure and algorithms, general programming, and bit manipulation, an important topic for interviews. You can also get this course on ZTM Academy and can use code FRIENDS10 to get 10% discount.
Top 15 Linked List Interview Questions and Solutions
Without any further ado, here is a list of Leetcode problems you can solve to get better at linked list:
- Reverse Linked List
Description: Given the head of a singly linked list, reverse the list and return its new head.
Hint: Use an iterative approach with three pointers (previous, current, next) to reverse the links.
Solution: see here - Linked List Cycle
Description: Detect if a cycle exists in a linked list.
Hint: Use two pointers (slow and fast); if they meet, a cycle exists.
Solution: see here - Merge Two Sorted Lists
Description: Merge two sorted linked lists and return it as a new sorted list.
Hint: Use a dummy node to simplify the merge process.
Solution: see here - Intersection of Two Linked Lists
Description: Find the node where two singly linked lists intersect.
Hint: Use two pointers starting at different lists; when they reach the end, switch to the other list.
Solution: see here - Remove Nth Node From End of List
Description: Remove the Nth node from the end of a list.
Hint: Use two pointers with the first pointer ahead by N nodes.
Solution: see here - Add Two Numbers
Description: Add two numbers represented by linked lists.
Hint: Simulate the addition process, node by node, and handle carry.
Solution: see here - Copy List with Random Pointer
Description: Create a deep copy of a linked list where each node has a random pointer.
Hint: Use a hash map to store the mapping between original and copied nodes.
Solution: see here - Flatten a Multilevel Doubly Linked List
Description: Flatten a multilevel doubly linked list so that all nodes appear in a single-level doubly linked list.
Hint: Use a stack to manage the nodes at different levels.
Solution: see here - Rotate List
Description: Rotate the list to the right by k places.
Hint: Connect the end of the list to the head, then break the connection after the new tail.
Solution: see here - Sort List
Description: Sort a linked list in O(n log n) time using constant space complexity.
Hint: Use merge sort or quick sort algorithm.
Solution: see here - Remove Duplicates from Sorted List II
Description: Remove all elements from a sorted linked list that have duplicate numbers, leaving only distinct numbers.
Hint: Use two pointers to track the unique elements.
Solution: see here - LRU Cache
Description: Design and implement a data structure for a Least Recently Used (LRU) cache.
Hint: Use a combination of a hash map and a doubly linked list.
Solution: see here - Design Browser History
Description: Design a browser history system where you can visit a URL, go back, and move forward.
Hint: Use two stacks to manage the back and forward history.
Solution: see here - Merge k Sorted Lists
Description: Merge k sorted linked lists into one sorted list.
Hint: Use a min-heap to efficiently merge lists.
Solution: see here - Reverse Nodes in k-Group
Description: Reverse the nodes of a linked list k at a time and return the modified list.
Hint: Reverse k nodes at a time, then connect them back to the previous part.
Solution: see here - How to find the middle element of a linked list in single pass in Java? (solution)
- How to find length of a singly linked list? (solution)
And, if you need more questions, you can also see my earlier articles on linked list coding problems
Tips to Solve Linked List Coding Problems
And, here are few tips you can use to solve these Leetcode problems to get better at Linked List
1. Understand the Basics
- Make sure you have a solid understanding of the basic structure of a linked list, including nodes and pointers.
- Know the differences between singly and doubly linked lists, as well as circular linked lists.
2. Practice Common Operations
- Familiarize yourself with common operations such as insertion, deletion, and traversal.
- Practice reversing a linked list, finding the middle element, and detecting cycles.
3. Use Multiple Pointers
- Many linked list problems can be solved using multiple pointers, such as the slow and fast pointer technique for cycle detection.
- Use a dummy node to simplify edge cases when merging lists or removing elements.
4. Practice Recursion
- Many linked list problems, like reversing in groups, can be elegantly solved using recursion.
- Understand how to convert recursive solutions to iterative ones and vice versa.
5. Think About Edge Cases
- Consider edge cases such as empty lists, lists with only one node, and lists with cycles.
- Ensure your solution handles these cases gracefully.
6. Visualize the Problem
- Draw diagrams to visualize the linked list and the changes you need to make.
- This can help you understand the problem better and plan your approach.
7. Optimize for Time and Space
- Aim to solve problems with optimal time and space complexity.
- Avoid unnecessary operations and use auxiliary space only when necessary.
8. Write Clean and Modular Code
- Break down your solution into smaller, manageable functions.
- Write clean and readable code with meaningful variable names and comments.
9. Test Your Solution
- Test your code with different test cases, including edge cases.
- Use assertions or print statements to verify the correctness of your solution.
10. Learn from Examples
- Study and understand solutions to common linked list problems.
- Analyze why certain approaches work and how they can be adapted to solve similar problems.
11. Stay Calm and Patient:
- Linked list problems can be tricky and require careful manipulation of pointers.
- Stay calm, be patient, and systematically debug your code when things don’t work as expected.
By following these tips and practicing regularly, you’ll become proficient at solving linked list problems and be well-prepared for technical interviews. You can also see a course like Grokking the Coding Interview: Patterns for Coding Questions from DeisgnGuru.io where you can learn coding patterns like fast and slow pointers which can be used to solve multiple Leetcode problem related to linked list.
More Coding Interview Resources
If you need recommendations, following are some of my the tried and tested resources to learn Data Structure and Algorithms in-depth:
- Data Structures and Algorithms: Deep Dive Using Java for Java developers
- Algomonster, a coding interview website created by ex Google engineers to help you with cracking FAANG interviews.
- Algorithms and Data Structures in Python for those who love Python
- Grokking the Coding Interview: Patterns for Coding Questions on DesignGuru.io to master coding patterns which can be used to solve 100+ Leetcode problems.
- JavaScript Algorithms and Data Structures Masterclass by Colt Steele for JavaScript programmers
- Mastering Data Structures & Algorithms using C and C++ for those who are good at C/C++
- Data Structures in Java: An Interview Refresher to refresh important Data Structure and algorithms concepts in Java.
And, if you prefer books, there is no better than Introduction to Algorithms by Thomas H. Cormen. It’s one of the most comprehensive books on Data Structure and Algorithms.
That’s all about the top 15 Leetcode problems to get better at Linked List. Mastering these linked list problems will not only prepare you for common interview questions but also strengthen your overall understanding of linked list operations and techniques.
Practice these problems, understand the underlying concepts, and you’ll be ready to tackle any linked list challenges in your technical interviews. Good luck!
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Thanks for reading this article so far. If you like these Leetcode Linked List problems then please share with your friends and colleagues. If you have any question or feedback then please drop a note.
P.S. — If you prefer books then you can also check out my list of top 10 books to prepare coding interviews.
