Solved LeetCode 22. Generate Parentheses using Backtracking in Java

#Day45 of #50DaysOfCoding Divisible Sum Pairs Problem (Java) Today, I tackled the “Divisible Sum Pairs” problem from HackerRank using Java. The objective was to identify all pairs of numbers in a list whose sum is divisible by a specified integer k. Concepts Used: - Nested loops to check every unique pair (i, j) where i < j. - Modulo operation to verify divisibility: (ar[i] + ar[j]) % k == 0. - Basic iteration and condition checking logic. Working: - Read input values n, k, and the array ar. - Iterate through all pairs. - Count how many pairs have sums divisible by k. - Print the total count. Example: If n = 6, k = 3, and ar = [1, 3, 2, 6, 1, 2], the valid pairs are (1,2), (3,6), (2,4), etc. Output: 5 Complexity: - Time Complexity: O(n²) - Space Complexity: O(1) This exercise enhanced my understanding of modulo operations, loops, and pair iteration logic — essential concepts for many coding interviews. #Java #ProblemSolving #CodingJourney #Programming #LearningEveryday #LogicBuilding #leetcode #DSA #CodingChallenge #LearnJava #CodeNewbie #Algorithms #DataStructures #TechJourney #javaProgramming #LearningInPublic #PentagonSpace

🚀 Day 29 of 100 Days of LeetCode 📘 Problem: Combination Sum 💻 Language: Java ✅ Status: Accepted — Runtime ⚡ 2 ms (Beats 86%) Today’s problem was all about backtracking — exploring all possible combinations to reach a target sum. It’s a perfect blend of recursion, decision-making, and pruning unnecessary paths 🧠 ✨ Key Learnings: Backtracking is like exploring a maze — try, backtrack, and try again until you find the exit 🌀 Each recursive call represents a “choice point” — include or skip the element Clean recursion with controlled base cases leads to clarity and precision This problem reminded me how persistence works in both code and life: 💬 “Sometimes, the path to the solution is not straightforward — you just need to keep exploring.” #Day29 #100DaysOfCode #LeetCode #Java #Backtracking #Recursion #DSA #ProblemSolving #CodingJourney #SoftwareDevelopment #KeepLearning #CodeEveryday

Today, I explored one of the most important concepts in Java — the Collection Framework. It plays a major role in handling and manipulating groups of objects efficiently. Here’s what I learned 👇 ✅ Collection Interface – The root interface for working with groups of objects. ✅ List Interface – Allows duplicate elements and maintains insertion order. Examples: ArrayList, LinkedList, Vector ✅ Set Interface – Does not allow duplicate elements. Examples: HashSet, LinkedHashSet, TreeSet ✅ Queue Interface – Used to hold elements in FIFO (First In, First Out) order. Examples: PriorityQueue, LinkedList ✅ Map Interface – Stores key-value pairs. Examples: HashMap, TreeMap, LinkedHashMap 💬 What I found interesting: ArrayList is great for fast access but slower in insert/delete. LinkedList is better for frequent insertions/deletions. HashSet and HashMap provide excellent performance for lookups. 📚 The Java Collection Framework makes data handling more flexible, powerful, and clean — a must-know for every Java developer. #Java #Collections #1000010000 Coders#Programming #Learning #SoftwareDevelopment #CodingJourney

🚀 Day 18/100 of #100DaysOfCode ✅ Solved “Isomorphic Strings” (LeetCode #205) using Java! 🧩 Problem: Given two strings s and t, determine if they are isomorphic. 👉 Two strings are isomorphic if characters in one string can be replaced to get the other — while keeping order and unique mapping intact. 🧠 Approach: Used a HashMap to store the mapping of characters from s → t. Checked if each character in s has a consistent mapping in t. Also ensured that no two characters in s map to the same character in t. ✨ Example: s = "egg", t = "add" → true (e→a, g→d) s = "foo", t = "bar" → false 📈 Complexity: Time: O(n) Space: O(n) 💡 Key Learnings: Understood how to maintain one-to-one character mapping using a HashMap. Reinforced logic building for pattern matching between strings. 💻 Tech Used: Java | HashMap | Problem Solving #LeetCode #100DaysOfCode #Java #ProblemSolving #DSA #CodingJourney #LearnByDoing #DevCommunity

🚀 Day 27 of 100 Days of LeetCode 📘 Problem: Generate Parentheses 💻 Language: Java ✅ Status: Accepted — Runtime: ⚡ 0 ms (Beats 100%) Today’s challenge focused on backtracking, one of the most elegant and powerful problem-solving techniques in DSA. The task was to generate all possible valid combinations of parentheses — a perfect test of recursion and logical constraints 🧩 ✨ Key Learnings: Backtracking is about exploring all possibilities, then undoing choices when needed 🔄 Understanding base cases clearly makes recursion much easier Clean recursive structures lead to elegant and efficient solutions This problem reinforced one important principle — 🧠 “Sometimes, going back is the only way to move forward — both in code and in life.” #Day27 #100DaysOfCode #LeetCode #Java #Backtracking #Recursion #ProblemSolving #CodingJourney #DSA #SoftwareDevelopment #KeepLearning #CodeEveryday

🚀 Day 55 of #100DaysOfCode Challenge Problem: LeetCode #219 – Contains Duplicate II Language: Java ☕ Today I solved an interesting array problem that checks whether a duplicate element exists within a given distance k in the array. 💡 Logic: Use a HashMap to remember the last index of each number. If the same number appears again, check if the difference between indices ≤ k. If yes → return true, else keep checking. 💻 Code: import java.util.HashMap; public class Solution { public boolean containsNearbyDuplicate(int[] nums, int k) { HashMap<Integer, Integer> map = new HashMap<>(); for (int i = 0; i < nums.length; i++) { if (map.containsKey(nums[i]) && i - map.get(nums[i]) <= k) { return true; } map.put(nums[i], i); } return false; } } 🧠 Example: Input: [1,2,3,1], k = 3 Output: true ✅ (same number 1 appears within distance 3) ⚙️ Key Concepts: HashMap for quick lookup Difference check using indices Time Complexity → O(n) Space Complexity → O(n) 💬 Every day’s problem teaches me something new — today it was about using maps smartly to track elements efficiently. On to the next challenge! 💪 #Day55 #LeetCode #Java #100DaysOfCode #CodingJourney #ProblemSolving #HashMap #DSA

🚀 Day 55 of #100DaysOfCode Challenge Problem: LeetCode #219 – Contains Duplicate II Language: Java ☕ Today I solved an interesting array problem that checks whether a duplicate element exists within a given distance k in the array. 💡 Logic: Use a HashMap to remember the last index of each number. If the same number appears again, check if the difference between indices ≤ k. If yes → return true, else keep checking. 💻 Code: import java.util.HashMap; public class Solution { public boolean containsNearbyDuplicate(int[] nums, int k) { HashMap<Integer, Integer> map = new HashMap<>(); for (int i = 0; i < nums.length; i++) { if (map.containsKey(nums[i]) && i - map.get(nums[i]) <= k) { return true; } map.put(nums[i], i); } return false; } } 🧠 Example: Input: [1,2,3,1], k = 3 Output: true ✅ (same number 1 appears within distance 3) ⚙️ Key Concepts: HashMap for quick lookup Difference check using indices Time Complexity → O(n) Space Complexity → O(n) 💬 Every day’s problem teaches me something new — today it was about using maps smartly to track elements efficiently. On to the next challenge! 💪 #Day55 #LeetCode #Java #100DaysOfCode #CodingJourney #ProblemSolving #HashMap #DSA

🚀 Day 55 of #100DaysOfCode Challenge Problem: LeetCode #219 – Contains Duplicate II Language: Java ☕ Today I solved an interesting array problem that checks whether a duplicate element exists within a given distance k in the array. 💡 Logic: Use a HashMap to remember the last index of each number. If the same number appears again, check if the difference between indices ≤ k. If yes → return true, else keep checking. 💻 Code: import java.util.HashMap; public class Solution { public boolean containsNearbyDuplicate(int[] nums, int k) { HashMap<Integer, Integer> map = new HashMap<>(); for (int i = 0; i < nums.length; i++) { if (map.containsKey(nums[i]) && i - map.get(nums[i]) <= k) { return true; } map.put(nums[i], i); } return false; } } 🧠 Example: Input: [1,2,3,1], k = 3 Output: true ✅ (same number 1 appears within distance 3) ⚙️ Key Concepts: HashMap for quick lookup Difference check using indices Time Complexity → O(n) Space Complexity → O(n) 💬 Every day’s problem teaches me something new — today it was about using maps smartly to track elements efficiently. On to the next challenge! 💪 #Day55 #LeetCode #Java #100DaysOfCode #CodingJourney #ProblemSolving #HashMap #DSA

🚀 Ever wondered how Java handles massive amounts of data so efficiently? It’s all thanks to the Java Collections Framework — one of the most powerful and versatile parts of the language! In this document, I’ve compiled everything you need to master Collections: ✅ Key differences between Arrays and Collections ✅ Clear hierarchy of Collection, List, Queue, Set, and Map ✅ Practical examples — ArrayList, LinkedList, Vector, Stack, HashSet, TreeSet, HashMap, TreeMap, and more ✅ Smart comparisons — ArrayList vs LinkedList, Comparable vs Comparator ✅ Hands-on Java exercises for real learning and interview prep Whether you're starting your Java journey or sharpening your coding edge, this guide gives you both clarity and confidence to handle data structures like a pro. 💬 Curious to know — which Collection do you use most in your projects? ArrayList, HashMap, or TreeSet? Follow for more practical Java insights! #Java #Collections #Coding #Programming #DataStructures #Learning #InterviewPreparation #SoftwareDevelopment #JavaDeveloper #CodingCommunity