Merging k Sorted Lists with Java and Heap

Day 44/100 – #100DaysOfCode 🚀 | #Java #LinkedList ✅ Problem Solved: Reverse Nodes in k-Group (LeetCode 25) 🧩 Problem Summary: Given a linked list, reverse every group of k consecutive nodes. If the last group has fewer than k nodes, leave it as is. 💡 Approach Used: We first count whether k nodes exist — only then we reverse that segment. Steps: Traverse ahead k nodes to ensure reversal is possible. Reverse exactly k nodes iteratively. Recursively process the remaining list. Connect the reversed part with the next processed segment. This allows efficient in-place operations without extra memory. ⚙️ Time Complexity: O(n) 📦 Space Complexity: O(1) (Reversing done in-place) ✨ Takeaway: This problem strengthens understanding of pointer manipulation and linked list segment handling — vital for clean and bug-free list operations. #Java #LinkedList #Pointers #Recursion #LeetCode #ProblemSolving #100DaysOfCode #CodingChallenge

Day 39/100 – #100DaysOfCode 🚀 | #Java #LeetCode #HashMap ✅ Problem Solved: Minimum Index Sum of Two Lists 🧩 Problem Summary: Given two string arrays, find the common strings with the smallest index sum (index in list1 + index in list2). If multiple answers exist, return all of them. 💡 Approach Used: ➤ Stored the elements of the first list in a HashMap with their indices. ➤ Iterated the second list and checked for matches. ➤ Tracked the minimum index sum and collected all strings that match that sum. This avoids nested loops and improves efficiency. ⚙️ Time Complexity: O(n + m) 📦 Space Complexity: O(n) ✨ Takeaway: HashMaps continue to be one of the most effective tools for reducing time complexity through direct lookups 🔍⚡ #Java #LeetCode #HashMap #DataStructures #ProblemSolving #100DaysOfCode #CodingJourney

🚀 Java Collections: Iterator vs ListIterator — Traversing the Smart Way Once we store data in a Collection, the next big question is: 👉 How do I access or modify each element efficiently? That’s where Iterator and ListIterator come in! 💡 Quick Tip: ✅ Use Iterator for generic collections. ✅ Use ListIterator when you need more control over a list. 📄 Check out this short PDF guide to visualize both in action 👇 #Java #Collections #ListIterator #Iterator #JavaDeveloper #BackendDevelopment #SpringBoot #CodingTips #DattatrayBharde

Where does your technical debt really hide? Cyclomatic complexity, churn, coupling — Richard Gross demonstrates how to measure and visualize deep problems in large codebases objectively. Read now on JAVAPRO: https://lnkd.in/eENXrUwD #Java #DomainDrivenDesign #LegacyCode

🚀 Inheritance (Java) Inheritance is a mechanism where a new class (subclass or derived class) inherits properties and behaviors from an existing class (superclass or base class). It promotes code reusability and establishes an 'is-a' relationship between classes. Subclasses can override methods from the superclass to provide specialized implementations. Inheritance supports the creation of class hierarchies, making the code more organized and maintainable. It's a powerful tool for modeling real-world relationships and reducing code duplication. #Java #JavaDev #OOP #Backend #professional #career #development

🔒 Understanding the final keyword in Java The final keyword adds safety and stability to your code by preventing unwanted changes. It can be used in three main ways: 🧩 With Variables – once assigned, the value can’t be changed. 🧩 With Methods – prevents overriding in subclasses. 🧩 With Classes – stops inheritance altogether. Simple yet powerful — final protects what’s meant to stay constant. #Java #OOPs #finalKeyword #JavaConcepts #CodingBasics #LearnJava

🚀#Day29 of my #120DaysOfCodingChallenge in #JavaFullStack 🎯 Today’s Concept: String vs StringBuffer in Java In Java, String and StringBuffer are used to handle text data, but they differ in how they store and modify values. Understanding the difference helps in choosing the right one for efficient and optimized memory usage. 💡 Key Points I Learned: 🔹 String is Immutable Once created, its value cannot be changed. If we try to change it, a new object is created in memory. 🔹 StringBuffer is Mutable Its value can be changed without creating new objects. It is used when frequent modifications or updates are required. 🔹 Performance Difference String → slower for repeated modifications. StringBuffer → faster and memory-efficient in such cases. 🔹 Usage Use String when the value is constant. Use StringBuffer when the text changes often (ex: loops, dynamic data). 🧠 Learning Outcome: This concept helped me understand how memory management works in Java when handling text. Choosing the right type improves performance and makes code more efficient and scalable. 🙏 A big thanks to my mentor Anand Kumar Buddarapu Sir for continuous guidance throughout this journey 🙌 #Java #String #StringBuffer #MemoryManagement #OOPS #JavaFullStack #CleanCode #LearningJourney #120DaysOfCodingChallenge

🔒 SynchronizedMap vs ConcurrentHashMap — What’s the Difference? While working on a Java project, I came across a classic concurrency question — Should I use Collections.synchronizedMap() or ConcurrentHashMap? 🤔 Here’s what I learned 👇 🧩 1️⃣ SynchronizedMap It wraps a normal Map (like HashMap) and synchronizes every method. This means only one thread can access the map at a time. It causes performance bottlenecks under high concurrency. Even iteration needs manual synchronization to avoid ConcurrentModificationException. 🧠 Example: Map<String, String> map = Collections.synchronizedMap(new HashMap<>()); ⚡ 2️⃣ ConcurrentHashMap Designed specifically for multi-threaded environments. Uses segment-based locking (Java 7) or lock-striping (Java 8) — allowing concurrent reads and partial writes. Iterators are fail-safe — they don’t throw ConcurrentModificationException. Much faster than SynchronizedMap under heavy load. 💻 Example: ConcurrentHashMap<String, String> map = new ConcurrentHashMap<>(); ✅ In short: Use SynchronizedMap → Simple synchronization, low concurrency. Use ConcurrentHashMap → High-performance concurrent access. 💡 Choose the right one based on your use case — performance and thread safety can make a big difference! #Java #ConcurrentHashMap #Multithreading #SynchronizedMap #SpringBoot #JavaDeveloper #LearningJourney

Day 29/100 – #100DaysOfCode 🚀 | #Java #LeetCode #BinaryTree ✅ Problem Solved: Verify Preorder Serialization of a Binary Tree 🌲 🧩 Problem Summary: Given a string representing a preorder serialization of a binary tree, determine if it’s valid. Example: "9,3,4,#,#,1,#,#,2,#,6,#,#" → ✅ valid "1,#" → ❌ invalid 💡 Approach Used: Used the slot-counting method 🧠 Each node uses one slot and non-null nodes create two new slots. Process the preorder string, ensuring slots never go negative and exactly zero remain at the end. ⚙️ Time Complexity: O(n) 📦 Space Complexity: O(1) ✨ Takeaway: This problem teaches how binary tree structure can be validated with simple counting logic — no need to rebuild the tree! 🌱 #Java #LeetCode #BinaryTree #100DaysOfCode #ProblemSolving #CodingChallenge

Wrapped up a few Java programs recently focused on input/output handling and conditional logic. The goal wasn’t just to get them working, but to make them maintainable — clear structure, meaningful variable names, and minimal redundancy. Writing clean code early builds the mindset for building scalable systems later. #Java #SoftwareEngineering #CleanCode