Mastering Deque + Sliding Window in Java for Coding Interviews

Two Pointer Technique: Today I explored the Two Pointer approach in Java, and it completely changed how I look at array problems 👇 🔹 Instead of using nested loops (O(n²)), we can solve many problems in O(n) using two pointers. 💡 Basic Idea: - Use two pointers (left & right) - Move them based on conditions - Reduce unnecessary iterations 📌 Example: Move Zeroes - Keep a slow pointer for non-zero elements - Traverse with a fast pointer - Swap when needed This simple technique makes code more efficient and clean 🔥 Still learning, but improving step by step 💪 👉 What other problems can be solved using two pointers? Today I practiced the Two Pointer approach in Java using the "Move Zeroes" problem 👇 💡 Idea: - Use a slow pointer to track position of non-zero elements - Use a fast pointer to traverse the array - Swap when needed 🧠 Java Code: public class MoveZeroes { public static void moveZeroes(int[] arr) { int slow = 0; for (int fast = 0; fast < arr.length; fast++) { if (arr[fast] != 0) { int temp = arr[slow]; arr[slow] = arr[fast]; arr[fast] = temp; slow++; } } } public static void main(String[] args) { int[] arr = {1, 2, 0, 4, 3, 0, 5, 0}; moveZeroes(arr); for (int num : arr) { System.out.print(num + " "); } } } ⚡ Time Complexity: O(n) ⚡ Space Complexity: O(1) Small step, but feels great to understand optimization like this 🔥 👉 Any better approaches or suggestions? #Java #DSA #TwoPointers #LearningInPublic #CodingJourney

🚀 Day 55: The Power of Polymorphism in Java 🎭 Today was a deep dive into one of the most powerful concepts in Object-Oriented Programming: Polymorphism (Greek for "Many Forms"). It’s the ability of an object to take on different forms depending on the context.   In Java, I learned that this flexibility happens at two distinct stages: 1. Compile-Time Polymorphism (Static Binding) ⏱️ This is achieved through Method Overloading.  ▫️ The Logic: Defining multiple methods in the same class with the same name but different parameters (type, number, or order). ▫️ The Benefit: It improves code readability and allows us to perform similar operations with different types of data without inventing new method names. Why "Compile-Time"? The compiler knows exactly which method to call just by looking at the arguments you provide. 2. Runtime Polymorphism (Dynamic Binding) 🏃♂️ This is achieved through Method Overriding.  ▫️ The Logic: When a subclass provides a specific implementation of a method that is already defined in its parent class. ▫️ The Magic: We use Upcasting (Parent class reference pointing to a Child class object). The specific version of the method to be executed is determined while the program is actually running. ▫️ The Benefit: This is the secret to building flexible, scalable systems where you can add new features without breaking existing code. Question for the Java Community: In your experience, what’s a real-world scenario where Runtime Polymorphism saved you from writing massive if-else or switch blocks? I’d love to hear your examples! 👇 #Java #OOPs #Polymorphism #100DaysOfCode #BackendDevelopment #CleanCode #SoftwareEngineering #LearningInPublic #JavaDeveloper 10000 Coders Meghana M

#Day45 – Map in Java: Key-Value Pairs & Problem Solving -#Programming ⚠️ Today, I explored one of the most powerful data structures in Java — Map, which helps in storing data in key-value pairs and solving real-world problems efficiently. 💡 Key Learnings: ✔ Map → collection of key-value pairs ✔ Key → unique (no duplicates allowed) and Value → can have duplicates ✔ One key maps to exactly one value ✔ Methods: put(), get(), remove(), containsKey(), containsValue() ✔ keySet() → get all keys , values() → get all values ✔ entrySet() → get key-value pairs , size() and isEmpty() ✔ Types of Map → HashMap, LinkedHashMap, TreeMap ✔ HashMap → no order , LinkedHashMap → maintains insertion order ✔ TreeMap → sorts keys 🧠 Example Solved: Solved a problem to count the frequency of each character in a string (e.g., Mississippi → M1i4s4p2) using Map. Learned how to efficiently track occurrences using containsKey(), get(), and put() methods. A big thank you to TAP Academy, Harshit T Sir, and Somanna M G Sir for explaining complex concepts in such a simple and practical way. Your teaching style, real-world examples, and constant support have made a huge difference in my understanding of Java and problem-solving. 🙏 #Java #CollectionsFramework #Map #HashMap #LinkedHashMap #DataStructures #CodingJourney #Consistency

LeetCode in Java: Longest Harmonious Subsequence I recently solved the Longest Harmonious Subsequence problem using Java, and here’s what stood out: 🔹 Approach: Built a HashMap<Integer, Integer> to store frequencies of each number. Iterated through keys to check if num + 1 exists. Calculated subsequence length by combining counts of num and num + 1. Tracked the maximum length across all valid pairs. 📊 Test Case:nums = [1,3,2,2,5,2,3,7]✅ Output: 5 Key Takeaways: Java’s explicit structure makes frequency mapping and iteration very clear. Practicing in Java strengthens problem-solving skills for interviews, especially when dealing with collections and edge cases. Reinforces the importance of thinking in terms of data structures + algorithmic logic rather than just syntax.

In this article, we will cover everything you need to know about Java multithreading — from basic thread creation to advanced concepts like. You can structure your article like this: 🔹 Introduction to Java Multithreading 🔹 Ways to Create Threads in Java 🔹 Thread Lifecycle Explained 🔹 sleep() vs wait() vs notify() 🔹 yield(), join(), and interrupt() 🔹 ThreadLocal in Real-World Applications 🔹 CountDownLatch vs CyclicBarrier vs Semaphore 🔹 Locks in Java (ReentrantLock, ReadWriteLock, StampedLock) 🔹 synchronized vs Lock 🔹 Intrinsic Locks Explained. If you found this guide helpful, feel free to share it and follow for more deep-dive articles on Java and backend development. #Java #Multithreading #JavaDeveloper #BackendDevelopment #Concurrency #SpringBoot #CodingInterview #SoftwareEngineering #JavaConcurrency #TechInterview

🚀 Understanding TreeSet in Java – Clean, Sorted & Powerful! While working with Java Collections, I explored TreeSet, a powerful implementation of the Set interface that ensures data is always sorted and unique. Here are some key insights I learned: 🔹 Sorted Order TreeSet automatically stores elements in ascending sorted order, making it ideal when ordering is important. 🔹 Traversal Mechanism It internally follows Inorder Traversal (LVR), which is why elements remain sorted. 🔹 Data Type TreeSet stores only homogeneous data, as elements must be mutually comparable. 🔹 No Duplicates Allowed Being a Set, it does not allow duplicate values. 🔹 No Null Values TreeSet does not allow null, as it relies on comparison logic. 🔹 Insertion Order Not Preserved Unlike some collections, it does not maintain insertion order. 🔹 Initial Capacity TreeSet does not define an initial capacity (internally managed). 🔹 Constructors TreeSet provides 5 different constructors for flexibility. 🔹 Internal Data Structure It is based on a Binary Search Tree (BST) (specifically a self-balancing tree like Red-Black Tree). 💡 Accessing Elements in TreeSet Since TreeSet does not support indexing, we use: ✔️ For-each loop ✔️ Iterator ✔️ Descending Iterator ❌ Not supported: Traditional for loop (index-based) ListIterator 🎯 When to Use TreeSet? Use TreeSet when you need: ✔️ Sorted data ✔️ Unique elements ✔️ Efficient searching and retrieval 📌 Mastering collections like TreeSet helps in writing cleaner and more efficient Java programs. #Java #CollectionsFramework #TreeSet #Programming #JavaDeveloper #LearningJourney TAP Academy

🚀 Mastering TreeSet in Java: Hierarchy & Powerful Methods While diving deeper into the Java Collections Framework, I explored the structure and capabilities of TreeSet—a class that combines sorting, uniqueness, and efficient navigation. 🔷 TreeSet Hierarchy (Understanding the Backbone) The hierarchy of TreeSet is what gives it its powerful features: 👉 TreeSet ⬇️ extends AbstractSet ⬇️ implements NavigableSet ⬇️ extends SortedSet ⬇️ extends Set ⬇️ extends Collection ⬇️ extends Iterable 💡 This layered structure enables TreeSet to support sorted data, navigation operations, and collection behavior seamlessly. 🔷 Important Methods in TreeSet TreeSet provides several methods for efficient data handling and navigation: 📌 Basic Retrieval first() → Returns the first (smallest) element last() → Returns the last (largest) element 📌 Range Operations headSet() → Elements less than a given value tailSet() → Elements greater than or equal to a value subSet() → Elements within a specific range 📌 Removal Operations pollFirst() → Removes and returns first element pollLast() → Removes and returns last element 📌 Navigation Methods ceiling() → Smallest element ≥ given value floor() → Largest element ≤ given value higher() → Element strictly greater than given value lower() → Element strictly less than given value 🔷 When to Use TreeSet? TreeSet is the right choice when you need: ✔️ Sorted Order (automatic ascending order) ✔️ No Duplicate Entries ✔️ Efficient Range-Based Operations ✔️ Navigation through elements (closest matches) 📊 Time Complexity: Insertion → O(log n) Access/Search → O(log n) 💡 Key Insight: TreeSet internally uses a self-balancing tree (Red-Black Tree), which ensures consistent performance and sorted data at all times. 🎯 Understanding TreeSet not only strengthens your knowledge of collections but also helps in solving real-world problems involving sorted and dynamic datasets. #Java #TreeSet #JavaCollections #Programming #DataStructures #LearningJourney TAP Academy

Primitives vs. Objects in Java Why does some Java code turn purple in your IDE while other code stays black? It's not random—it's telling you something important. Primitive types like int, char, long, and double turn purple because they're baked directly into Java. They're the building blocks, the simplest forms of data the language recognizes. Objects like String don't get that color treatment because they're more complex structures. Here's the practical difference that matters: Objects give you access to the dot (.) operator—a key that unlocks built-in methods. With a String, you can call .toUpperCase(), .toLowerCase(), .length(), and dozens of other methods that manipulate your data. Primitives? They just hold a value. No dot, no methods, no extras. Once you understand this distinction, you'll start reading your IDE's color coding like a second language. Did you know this difference when you started? Drop a 🟣 if this clicked something for you. #java

🚀 LeetCode #496 – Next Greater Element I | Java Solution Today’s problem was a great introduction to Stacks + HashMaps — a powerful combination for optimizing search problems 🔥 📌 Problem Summary Given two arrays nums1 and nums2 (where nums1 is a subset of nums2), find the next greater element for each element in nums1 from nums2. 👉 The next greater element is the first element to the right that is larger than the current number. 💡 Approach I Used (Optimized – O(n)) Traverse nums2 using a monotonic decreasing stack For each element: If current element > stack top → it's the "next greater" Store mapping in a HashMap Finally, build result for nums1 using the map 💻 Java Code Snippet int[] arr = new int[n1.length]; Stack<Integer> stk = new Stack<>(); HashMap<Integer,Integer> map = new HashMap<>(); for(int i = 0; i < n2.length; i++){ while(!stk.isEmpty() && n2[i] > stk.peek()){ map.put(stk.pop(), n2[i]); } stk.push(n2[i]); } for(int j = 0; j < n1.length; j++){ arr[j] = map.getOrDefault(n1[j], -1); } 🧠 Key Learning Understanding Monotonic Stack Reducing brute force O(n²) → O(n) Using HashMap for quick lookups 📊 Example nums1 = [4,1,2] nums2 = [1,3,4,2] Output = [-1,3,-1] 🔥 Why this problem matters? Frequently asked in interviews Builds foundation for problems like: Daily Temperatures Stock Span Next Greater Element II Happy Coding 😊 #LeetCode #Java #DSA #Stack #CodingJourney #ProblemSolving #100DaysOfCode #Algorithms

Polymorphism in Java Polymorphism is one of the core concepts of Object-Oriented Programming (OOP). It allows a single method name to perform different tasks based on the input. Types of Polymorphism in Java: 1. Compile-Time Polymorphism (Static Binding)→ Achieved using Method Overloading. 2. Run-Time Polymorphism (Dynamic Binding)→ Achieved using Method Overriding. Today I Learned: 1. Compile-Time Polymorphism in Java Today I explored the concept of Compile-Time Polymorphism, also known as Method Overloading in Java. It allows a class to have multiple methods with the same name but different parameters (type, number, or order). The method call is resolved at compile time, which makes the execution faster and more efficient. Example: Calculator using Method Overloading. This concept improves code readability and helps in writing flexible and reusable code. #Java #OOP #Polymorphism #MethodOverloading #LearningJourney