This repository is dedicated to helping you master the essential data structures and algorithms that are crucial for technical interviews, particularly in the context of coding challenges and competitive programming. Whether you're preparing for your next job interview or looking to level up your problem-solving skills, you'll find a collection of the most commonly asked problems along with effective learning resources.
- Detailed Problem Solutions: A comprehensive list of LeetCode problems organized by category and difficulty to help you build your skills step by step.
- Algorithms & Data Structures: Explore topics like Arrays, Hashing, Two Pointers, Sliding Window, Linked Lists, Trees, Stacks, Binary Search, and more!
- Helpful Resources: Direct links to tutorials, explanations, and articles to deepen your understanding of each topic, accompanied by problem sets that are frequently asked in interviews.
- Arrays & Hashing: Master the building blocks for many problems involving sequence and uniqueness.
- Two Pointers: Learn the technique used to optimize problems involving linear data structures.
- Sliding Window: Solve problems related to subarrays and subsequences efficiently.
- Stacks: Understand how to handle problems that require Last-In-First-Out (LIFO) access.
- Linked Lists: Dive deep into data structures that allow dynamic data storage and manipulation.
- Binary Search: Improve your ability to search in sorted data with logarithmic time complexity.
- Trees: Build a strong foundation in binary trees, binary search trees, and tree traversal algorithms.
Whether you're a beginner looking to get started with coding challenges or an experienced developer aiming to polish your interview prep, this collection is here to support your journey. Happy coding!
Here are some useful resources to help you understand the essential data structures and algorithms that frequently appear in technical interviews. Each section links to tutorials and articles for deeper learning.
- Introduction to Arrays
- Hashing in Data Structures
- LeetCode - Arrays and Hashing Problems
- Hashing Techniques
- Two Pointers Algorithm
- LeetCode - Two Pointers Problems
- Tutorial on Two Pointers Technique
- Two Pointers Algorithm Explanation
- Introduction to Binary Search
- Binary Search Algorithm Explained
- LeetCode - Binary Search Problems
- Binary Search Tutorial
- Sliding Window Technique
- Sliding Window Algorithm
- LeetCode - Sliding Window Problems
- Sliding Window Approach Explained
- Introduction to Linked Lists
- LeetCode - Linked List Problems
- Linked List Data Structure
- Linked List Tutorial
- Introduction to Binary Trees
- LeetCode - Tree Problems
- Binary Tree Traversal Algorithms
- Binary Search Trees (BST) Basics
Arrays and hashing are core topics in technical interviews. This section includes some of the most frequently asked LeetCode problems, helping you recognize patterns and build efficient solutions using arrays, hash sets, and hash maps.
| 🧩 Problem | ⚙️ Difficulty | 🔗 Link |
|---|---|---|
| Contains Duplicate | Easy | Link |
| Valid Anagram | Easy | Link |
| Two Sum | Easy | Link |
| Group Anagrams | Medium | Link |
| Top K Frequent Elements | Medium | Link |
| Encode and Decode Strings | Medium | Link |
| Product of Array Except Self | Medium | Link |
| Valid Sudoku | Medium | Link |
| Longest Consecutive Sequence | Hard | Link |
| Intersection of Two Arrays | Easy | Link |
| Contains Duplicate II | Easy | Link |
| Set Matrix Zeroes | Medium | Link |
| Spiral Matrix | Medium | Link |
| 3Sum | Medium | Link |
| 4Sum | Medium | Link |
| Subarray Sum Equals K | Medium | Link |
| Sliding Window Maximum | Hard | Link |
| Minimum Window Substring | Hard | Link |
| Longest Substring Without Repeating Characters | Medium | Link |
The Two Pointers technique is widely used to optimize algorithms, especially in array, string, and linked list problems. Many technical interviews test this pattern to evaluate your problem-solving and algorithmic skills.
| 🧩 Problem | ⚙️ Difficulty | 🔗 Link |
|---|---|---|
| Reverse String | Easy | Link |
| Valid Palindrome | Easy | Link |
| Remove Duplicates from Sorted Array | Easy | Link |
| Move Zeroes | Easy | Link |
| Two Sum II - Input Array Is Sorted | Easy | Link |
| Merge Sorted Array | Easy | Link |
| Linked List Cycle | Easy | Link |
| 3Sum | Medium | Link |
| Container With Most Water | Medium | Link |
| Sort Colors | Medium | Link |
| Remove Nth Node From End of List | Medium | Link |
| Partition List | Medium | Link |
| Trapping Rain Water | Hard | Link |
| Sliding Window Maximum | Hard | Link |
| Palindrome Linked List | Hard | Link |
Stacks are a fundamental data structure used to solve problems involving reverse order, nested structures, and backtracking. This section includes some of the most common LeetCode problems involving stacks, which are frequently asked in technical interviews.
| 🧩 Problem | ⚙️ Difficulty | 🔗 Link |
|---|---|---|
| Valid Parentheses | Easy | Link |
| Min Stack | Easy | Link |
| Next Greater Element I | Easy | Link |
| Daily Temperatures | Medium | Link |
| Generate Parentheses | Medium | Link |
| Car Fleet | Medium | Link |
| Remove Duplicate Letters | Medium | Link |
| Asteroid Collision | Medium | Link |
| Valid Parenthesis String | Medium | Link |
| Maximal Rectangle | Hard | Link |
| Largest Rectangle In Histogram | Hard | Link |
| Minimum Remove to Make Valid Parentheses | Medium | Link |
| Flatten Nested List Iterator | Medium | Link |
| Palindrome Linked List | Easy | Link |
| Reverse Substrings Between Each Pair of Parentheses | Medium | Link |
Binary Search is one of the most important algorithms to master, often used to optimize searching problems. This section includes a collection of LeetCode problems involving binary search, many of which are frequently asked in technical interviews at top companies.
| 🧩 Problem | ⚙️ Difficulty | 🔗 Link |
|---|---|---|
| Binary Search | Easy | Link |
| Search Insert Position | Easy | Link |
| First Bad Version | Easy | Link |
| Search a 2D Matrix | Medium | Link |
| Koko Eating Bananas | Medium | Link |
| Find Minimum In Rotated Sorted Array | Medium | Link |
| Search In Rotated Sorted Array | Medium | Link |
| Find Peak Element | Medium | Link |
| Perfect Squares | Medium | Link |
| Find the Duplicate Number | Medium | Link |
| Sqrt(x) | Easy | Link |
| Time Based Key-Value Store | Hard | Link |
| Median of Two Sorted Arrays | Hard | Link |
| Count of Smaller Numbers After Self | Hard | Link |
| Split Array Largest Sum | Hard | Link |
Sliding Window is a key technique for solving problems that involve searching for subarrays or substrings. It allows for optimizing problems that require traversing contiguous parts of a list or string efficiently. This section includes the most common LeetCode problems using this technique, frequently asked in technical interviews.
| 🧩 Problem | ⚙️ Difficulty | 🔗 Link |
|---|---|---|
| Best Time to Buy and Sell Stock | Easy | Link |
| Permutation In String | Medium | Link |
| Fruit Into Baskets | Medium | Link |
| Sliding Window Maximum | Hard | Link |
| Longest Repeating Character Replacement | Medium | Link |
| Minimum Window Substring | Hard | Link |
| Maximum Sum Subarray of Size K | Medium | Link |
| Subarray Product Less Than K | Medium | Link |
| Count Number of Nice Subarrays | Medium | Link |
| Number of Substrings Containing All Three Characters | Medium | Link |
| Subarrays of Size K with Average Greater than or Equal to Threshold | Medium | Link |
| Replace the Substring for Balanced String | Medium | Link |
Linked Lists are fundamental data structures used to store sequences of elements. This section includes LeetCode problems involving Linked Lists, which frequently appear in technical interviews. Mastering these problems will help you understand how to manipulate pointers and build efficient solutions.
| 🧩 Problem | ⚙️ Difficulty | 🔗 Link |
|---|---|---|
| Reverse Linked List | Easy | Link |
| Linked List Cycle | Easy | Link |
| Merge Two Sorted Lists | Easy | Link |
| Intersection of Two Linked Lists | Easy | Link |
| Remove Nth Node From End of List | Medium | Link |
| Reorder List | Medium | Link |
| Add Two Numbers | Medium | Link |
| Find the Duplicate Number | Medium | Link |
| Palindrome Linked List | Medium | Link |
| Flatten a Linked List | Medium | Link |
| Copy List With Random Pointer | Medium | Link |
| LRU Cache | Hard | Link |
| Linked List Cycle II | Hard | Link |
| Swap Nodes in Pairs | Medium | Link |
Trees are a crucial concept in computer science, often used to represent hierarchical data structures. This section includes common LeetCode problems related to binary trees, binary search trees, and tree traversal, which are frequently asked in technical interviews.
| 🧩 Problem | ⚙️ Difficulty | 🔗 Link |
|---|---|---|
| Maximum Depth of Binary Tree | Easy | Link |
| Same Tree | Easy | Link |
| Invert Binary Tree | Easy | Link |
| Balanced Binary Tree | Easy | Link |
| Diameter of Binary Tree | Medium | Link |
| Lowest Common Ancestor of a Binary Search Tree | Medium | Link |
| Subtree of Another Tree | Medium | Link |
| Binary Tree Level Order Traversal | Medium | Link |
| Path Sum | Medium | Link |
| Convert Sorted Array to Binary Search Tree | Medium | Link |
| Kth Smallest Element in a BST | Medium | Link |
| Validate Binary Search Tree | Hard | Link |
| Serialize and Deserialize Binary Tree | Hard | Link |