Curated DSA Interview Questions - Java Edition

The Ultimate Collection of Data Structures & Algorithms Problems for Interview Preparation

This repository contains a carefully curated collection of the most important and logic-building DSA problems specifically focusing on Arrays, Strings, and Linked Lists in Java. These problems are selected from top-tier repositories and are designed to prepare you for technical interviews at companies like Reqpedia and other top-tier organizations.

🎯 Repository Focus

This collection emphasizes:

• Quality over Quantity: Only the most important and frequently asked problems
• Pattern Mastery: Comprehensive coverage of essential algorithmic patterns
• Logic Building: Problems that enhance problem-solving and analytical thinking
• Interview Readiness: Real-world problems asked in technical interviews
• Java Implementation: All solutions and examples are in Java

📚 Problem Categories

🔢 Arrays

Essential patterns covered:

• Two Pointers, Sliding Window, Prefix/Suffix Sums
• Searching, Sorting, Binary Search variations
• Kadane's Algorithm, Subarray problems
• Array rotations, rearrangements, merging
• Frequency counting, majority elements

🔤 Strings

Essential patterns covered:

• Palindrome detection and manipulation
• Substring search and pattern matching (KMP, Rabin-Karp)
• Sliding window techniques
• Character counting and anagram detection
• String parsing and validation
• Edit distance and dynamic programming

🔗 Linked Lists

Essential patterns covered:

• Floyd's Cycle Detection Algorithm
• Linked List reversal and manipulation
• Two pointer techniques
• Merging and sorting operations
• Deep copying and complex operations
• Intersection and palindrome detection

📋 Curated Problem Set

#	Title	Difficulty	Pattern	Source Link	Notes	Solve Here
1	Two Sum	Medium	Hash Table + Array	GitHub	Foundation problem for hash table usage	LeetCode
2	3Sum	Medium	Two Pointers + Arrays	GitHub	Classic two-pointer technique, avoid duplicates	LeetCode
3	Trapping Rain Water	Hard	Two Pointers + Arrays	GitHub	Advanced two-pointer, multiple approaches	LeetCode
4	Maximum Subarray	Medium	Kadane's Algorithm	GitHub	Essential DP pattern for subarray problems	LeetCode
5	Container With Most Water	Medium	Two Pointers + Arrays	GitHub	Greedy two-pointer approach	LeetCode
6	Merge Intervals	Medium	Interval Merging	GitHub	Critical for interval-based problems	LeetCode
7	Rotate Array	Medium	Array Rotation	GitHub	Multiple rotation techniques	LeetCode
8	Search in Rotated Sorted Array	Medium	Binary Search + Arrays	GitHub	Advanced binary search variation	LeetCode
9	First Missing Positive	Hard	Array Manipulation	GitHub	In-place array modification technique	LeetCode
10	Next Permutation	Medium	Array Rearrangement	GitHub	Complex array manipulation logic	LeetCode
11	Longest Palindromic Substring	Medium	String + Palindrome	GitHub	Expand around center technique	LeetCode
12	Longest Substring Without Repeating Characters	Medium	Sliding Window + String	GitHub	Classic sliding window pattern	LeetCode
13	Minimum Window Substring	Hard	Sliding Window + String	GitHub	Advanced sliding window technique	LeetCode
14	Group Anagrams	Medium	Hash Table + String	GitHub	String sorting and grouping	LeetCode
15	Valid Palindrome	Easy	Two Pointers + String	GitHub	String normalization and validation	LeetCode
16	Implement strStr()	Medium	KMP Algorithm + String	GitHub	Pattern matching algorithms	LeetCode
17	Longest Common Prefix	Easy	String Manipulation	GitHub	String comparison techniques	LeetCode
18	String to Integer (atoi)	Medium	String Parsing	GitHub	Complex string parsing and validation	LeetCode
19	Palindrome Partitioning	Medium	Backtracking + String	GitHub	Backtracking with palindrome validation	LeetCode
20	Edit Distance	Hard	Dynamic Programming + String	GitHub	Classic DP for string transformation	LeetCode
21	Linked List Cycle	Easy	Floyd's Algorithm + LinkedList	GitHub	Essential cycle detection technique	LeetCode
22	Linked List Cycle II	Medium	Floyd's Algorithm + LinkedList	GitHub	Advanced cycle detection with position	LeetCode
23	Reverse Linked List II	Medium	LinkedList Reversal	GitHub	Partial linked list reversal	LeetCode
24	Merge Two Sorted Lists	Easy	LinkedList Merging	GitHub	Foundation for merge operations	LeetCode
25	Remove Nth Node From End of List	Medium	Two Pointers + LinkedList	GitHub	One-pass two-pointer technique	LeetCode
26	Intersection of Two Linked Lists	Easy	Two Pointers + LinkedList	GitHub	Elegant intersection detection	LeetCode
27	Add Two Numbers	Medium	LinkedList Arithmetic	GitHub	Digit-by-digit addition with carry	LeetCode
28	Copy List with Random Pointer	Medium	Deep Copy + LinkedList	GitHub	Complex linked list deep copying	LeetCode
29	Merge k Sorted Lists	Hard	Divide & Conquer + LinkedList	GitHub	Advanced merging with heap/divide-conquer	LeetCode
30	Sort List	Medium	Merge Sort + LinkedList	GitHub	Implementing merge sort on linked list	LeetCode

🏆 Why This Collection?

Comprehensive Pattern Coverage

Every essential algorithmic pattern is covered through carefully selected problems that build upon each other.

Interview-Tested Problems

All problems are frequently asked in technical interviews at top companies including Google, Amazon, Microsoft, and startups like Reqpedia.

Progressive Difficulty

Problems are arranged to build your understanding from fundamental concepts to advanced techniques.

Logic Building Focus

Each problem is chosen for its ability to enhance logical thinking and problem-solving skills.

High-Quality Sources

All problems are sourced from the most reputable and well-maintained repositories:

• doocs/leetcode: 34,429+ stars, exceptional quality and organization
• Blankj/awesome-java-leetcode: 8,714+ stars, Java-focused solutions
• LeetCode Official: Primary problem source with comprehensive test cases

🚀 How to Use This Repository

1. Start with the Pattern: Understand the underlying pattern for each problem category
2. Read the Problem Statement: Click on "Solve Here" links to read full problem descriptions
3. Study the Source Code: Visit GitHub links to see multiple solution approaches
4. Practice Implementation: Implement solutions in your preferred IDE
5. Analyze Complexity: Understand time and space complexity for each approach
6. Master Variations: Practice similar problems to reinforce patterns

📈 Learning Path

Beginner Path (Problems 1, 15, 17, 21, 24, 26)

Start with these foundational problems to build core understanding.

Intermediate Path (Problems 2-14, 18-19, 22-23, 25, 27-28)

Tackle these problems after mastering the basics.

Advanced Path (Problems 3, 9, 13, 20, 29-30)

Challenge yourself with these complex problems requiring deep algorithmic knowledge.

🎯 Interview Success Tips

1. Pattern Recognition: Focus on recognizing which pattern applies to new problems
2. Time Management: Practice solving problems within interview time constraints
3. Code Quality: Write clean, readable code with proper variable names
4. Edge Cases: Always consider and handle edge cases
5. Optimization: Start with brute force, then optimize step by step
6. Communication: Practice explaining your thought process clearly

🤝 Contributing

This is a curated collection focused on quality over quantity. While we welcome suggestions for critical problems that may be missing, please ensure any proposed additions:

• Are frequently asked in interviews
• Represent unique algorithmic patterns
• Provide significant learning value
• Have high-quality solutions available

📚 Additional Resources

• doocs/leetcode: Comprehensive multi-language solutions
• Blankj/awesome-java-leetcode: Java-specific implementations
• LeetCode Patterns: Pattern-based problem solving guides

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Happy Coding! 🚀 Master these 30 problems and you'll be well-prepared for any Array, String, or LinkedList question in your technical interviews.