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Java DSA Interview Prep - Top 50 Interview Questions

A curated collection of the top 50 "sure short" interview questions, organized by pattern and topic.

Project Structure

The project is organized by DSA topics to make it easy to navigate and study.

src/main/java/com/dsa/
├── arrays/                # Array-based problems
├── strings/               # String manipulation problems
├── linkedlists/           # Linked list implementations and problems
├── stacks/                # Stack-based problems
├── queues/                # Queue-based problems
├── trees/                 # Binary trees, BST, etc.
├── graphs/                # Graph algorithms
├── recursion/             # Recursive solutions
├── dynamicprogramming/    # DP problems
├── sorting/               # Sorting algorithms
├── searching/             # Searching algorithms
├── backtracking/          # Backtracking problems
├── twopointer/           # Two Pointer problems
└── slidingwindow/        # Sliding Window problems

Problem Index

Topic Problem Difficulty Link
Arrays Two Sum Easy Solution
Strings Valid Palindrome Easy Solution
Sorting Quick Sort Medium Solution
Searching Binary Search Easy Solution
Backtracking N-Queens Hard Solution
Graphs Course Schedule Medium Solution
DP Edit Distance Hard Solution
Trees Serialize & Deserialize Tree Hard Solution
Linked Lists Reverse Linked List Easy Solution
Stacks Valid Parentheses Easy Solution
Trees Max Depth of Binary Tree Easy Solution
Two Pointer Two Sum Sorted Easy Solution
Two Pointer 3Sum Medium Solution
Two Pointer Container With Most Water Medium Solution
Two Pointer Trapping Rain Water Hard Solution
Two Pointer Move Zeroes Easy Solution
Two Pointer Remove Duplicates Easy Solution
Two Pointer Sort Colors Medium Solution
Two Pointer Two Sum Less Than K Easy Solution
Two Pointer 3Sum Closest Medium Solution
Two Pointer 4Sum Medium Solution
Two Pointer Backspace String Compare Easy Solution
Two Pointer Is Subsequence Easy Solution
Two Pointer Longest Word in Dictionary Medium Solution
Two Pointer Partition Labels Medium Solution
Two Pointer Remove Element Easy Solution
Two Pointer Squares of Sorted Array Easy Solution
Two Pointer Reverse String Easy Solution
Two Pointer Valid Triangle Number Medium Solution
Two Pointer Boats to Save People Medium Solution
Two Pointer Longest Mountain in Array Medium Solution
Sliding Window Max Sum Subarray Easy Solution
Sliding Window Smallest Subarray with Sum Easy Solution
Sliding Window Longest Substring K Distinct Medium Solution
Sliding Window Fruits into Baskets Medium Solution
Sliding Window No-repeat Substring Medium Solution
Sliding Window Character Replacement Medium Solution
Sliding Window Replacing Ones Medium Solution
Sliding Window String Permutation Hard Solution
Sliding Window String Anagrams Hard Solution
Sliding Window Sliding Window Maximum Hard Solution
Sliding Window Longest Substring 2 Distinct Medium Solution
Sliding Window Minimum Window Substring Hard Solution
Sliding Window Subarrays with K Distinct Hard Solution
Sliding Window Binary Subarrays With Sum Medium Solution
Sliding Window Max Points From Cards Medium Solution
Sliding Window Grumpy Bookstore Owner Medium Solution
Sliding Window Longest Turbulent Subarray Medium Solution
Sliding Window Substrings All Three Chars Medium Solution
Sliding Window Count Nice Subarrays Medium Solution
Sliding Window Min Operations to Reduce X Medium Solution
Recursion Fibonacci Number Easy Solution
Recursion Subsets Medium Solution
DP Climbing Stairs Easy Solution
DP Coin Change Medium Solution
Recursion Factorial Easy Solution
Recursion Generate Parentheses Medium Solution
DP House Robber Medium Solution
DP Longest Common Subsequence Medium Solution
Linked Lists Merge Two Sorted Lists Easy Solution
Linked Lists Linked List Cycle Easy Solution
Trees Binary Tree Level Order Medium Solution
Trees Invert Binary Tree Easy Solution
Graphs Number of Islands Medium Solution
Matrix Spiral Matrix Medium Solution
Matrix Rotate Image Medium Solution
Heaps Kth Largest Element Medium Solution

How to Run

Each problem includes a main method with a test case. You can run any file individually:

mvn compile
java -cp target/classes com.dsa.arrays.TwoSum

Goals

  • Master common patterns (Two Pointers, Sliding Window, DFS/BFS, etc.)
  • Understand Time and Space Complexity.
  • Stay consistent — one problem every day.

About

A collection of Java solutions for frequently asked Data Structures and Algorithms (DSA) interview questions, covering topics like arrays, strings, stacks, linked lists, trees, and graphs with optimized approaches.

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