Mastering Coding Challenges

In the last 15 years, I have interviewed 800+ Software Engineers across Google, Paytm, Amazon & various startups. Here are the most actionable tips I can give you on how to approach  solving coding problems in Interviews  (My DMs are always flooded with this particular question) 1. Use a Heap for K Elements      - When finding the top K largest or smallest elements, heaps are your best tool.      - They efficiently handle priority-based problems with O(log K) operations.      - Example: Find the 3 largest numbers in an array.   2. Binary Search or Two Pointers for Sorted Inputs      - Sorted arrays often point to Binary Search or Two Pointer techniques.      - These methods drastically reduce time complexity to O(log n) or O(n).      - Example: Find two numbers in a sorted array that add up to a target.   3. Backtracking    - Use Backtracking to explore all combinations or permutations.      - They’re great for generating subsets or solving puzzles.      - Example: Generate all possible subsets of a given set.   4. BFS or DFS for Trees and Graphs      - Trees and graphs are often solved using BFS for shortest paths or DFS for traversals.      - BFS is best for level-order traversal, while DFS is useful for exploring paths.      - Example: Find the shortest path in a graph.   5. Convert Recursion to Iteration with a Stack      - Recursive algorithms can be converted to iterative ones using a stack.      - This approach provides more control over memory and avoids stack overflow.      - Example: Iterative in-order traversal of a binary tree.   6. Optimize Arrays with HashMaps or Sorting      - Replace nested loops with HashMaps for O(n) solutions or sorting for O(n log n).      - HashMaps are perfect for lookups, while sorting simplifies comparisons.      - Example: Find duplicates in an array.   7. Use Dynamic Programming for Optimization Problems      - DP breaks problems into smaller overlapping sub-problems for optimization.      - It's often used for maximization, minimization, or counting paths.      - Example: Solve the 0/1 knapsack problem.   8. HashMap or Trie for Common Substrings      - Use HashMaps or Tries for substring searches and prefix matching.      - They efficiently handle string patterns and reduce redundant checks.      - Example: Find the longest common prefix among multiple strings.   9. Trie for String Search and Manipulation      - Tries store strings in a tree-like structure, enabling fast lookups.      - They’re ideal for autocomplete or spell-check features.      - Example: Implement an autocomplete system.   10. Fast and Slow Pointers for Linked Lists      - Use two pointers moving at different speeds to detect cycles or find midpoints.      - This approach avoids extra memory usage and works in O(n) time.      - Example: Detect if a linked list has a loop.   💡 Save this for your next interview prep!

𝐇𝐨𝐰 𝐦𝐮𝐜𝐡 𝐃𝐒𝐀 𝐢𝐬 𝐞𝐧𝐨𝐮𝐠𝐡 𝐭𝐨 𝐜𝐫𝐚𝐜𝐤 𝐌𝐢𝐜𝐫𝐨𝐬𝐨𝐟𝐭, 𝐆𝐨𝐨𝐠𝐥𝐞 𝐨𝐫 𝐖𝐚𝐥𝐦𝐚𝐫𝐭? This is the most common DM which I get from juniors are, "Ma’am, I’ve solved 300+ questions but still can’t solve new ones. How many do I really need to do?" When I started, I had the same doubt. Some seniors said 300 questions, others said 500+ to be safe. So I rushed to hit those numbers. But here’s the truth it’s not about the count, it’s about the patterns. Once you master patterns, every new problem feels familiar. Here are the 15 patterns you must know for placements: 1. 𝐓𝐰𝐨 𝐏𝐨𝐢𝐧𝐭𝐞𝐫 𝐓𝐞𝐜𝐡𝐧𝐢𝐪𝐮𝐞 – Solve pair/relationship problems in arrays/linked lists. 2. 𝐒𝐥𝐢𝐝𝐢𝐧𝐠 𝐖𝐢𝐧𝐝𝐨𝐰 – Efficiently handle subarray/substring problems. 3. 𝐇𝐚𝐬𝐡𝐢𝐧𝐠 / 𝐅𝐫𝐞𝐪𝐮𝐞𝐧𝐜𝐲 𝐂𝐨𝐮𝐧𝐭𝐢𝐧𝐠 – O(1) lookups for counts, duplicates, mapping. 4. 𝐏𝐫𝐞𝐟𝐢𝐱 𝐒𝐮𝐦𝐬 – Answer range queries fast. 5. 𝐁𝐢𝐧𝐚𝐫𝐲 𝐒𝐞𝐚𝐫𝐜𝐡 (𝐚𝐧𝐝 𝐯𝐚𝐫𝐢𝐚𝐧𝐭𝐬) – For sorted arrays or monotonic conditions. 6. 𝐆𝐫𝐞𝐞𝐝𝐲 – Local choices that lead to global solutions. 7. 𝐃𝐲𝐧𝐚𝐦𝐢𝐜 𝐏𝐫𝐨𝐠𝐫𝐚𝐦𝐦𝐢𝐧𝐠 – Break down overlapping subproblems. 8. 𝐁𝐚𝐜𝐤𝐭𝐫𝐚𝐜𝐤𝐢𝐧𝐠 – Explore all possibilities (subsets, permutations). 9. 𝐁𝐅𝐒 – Shortest paths, level-by-level traversals. 10. 𝐃𝐅𝐒 – Explore all paths, detect cycles. 11. 𝐇𝐞𝐚𝐩 / 𝐓𝐨𝐩-𝐊 – Manage largest/smallest efficiently. 12. 𝐌𝐞𝐫𝐠𝐞 𝐈𝐧𝐭𝐞𝐫𝐯𝐚𝐥𝐬 – Handle overlaps in schedules. 13. 𝐔𝐧𝐢𝐨𝐧-𝐅𝐢𝐧𝐝 – Manage connectivity in graphs. 14. 𝐓𝐫𝐢𝐞 – Prefix-based search and storage. 15. 𝐌𝐨𝐧𝐨𝐭𝐨𝐧𝐢𝐜 𝐒𝐭𝐚𝐜𝐤 / 𝐐𝐮𝐞𝐮𝐞 – Solve next/previous greater/smaller problems. And remember, DSA is not a sprint, it is a marathon. Rejections will happen, and that is normal. But every attempt makes you sharper, and every failure teaches you a pattern in life too. #DSA #Placements #CodingInterviews #ProblemSolving #CareerAdvice

Clean code is nice. But scalable architecture? That’s what makes you irreplaceable. Early in my journey, I thought “writing clean code” was enough… Until systems scaled. Teams grew. Bugs multiplied. That’s when I discovered Design Patterns, and things started making sense. Here’s a simple breakdown that can save you hundreds of hours of confusion. 🔷 Creational Patterns: Master Object Creation These patterns handle how objects are created. Perfect when you want flexibility, reusability, and less tight coupling. 💡 Use these when: You want only one instance (Singleton) You need blueprints to build complex objects step-by-step (Builder) You want to switch object types at runtime (Factory, Abstract Factory) You want to duplicate existing objects efficiently (Prototype) 🔷 Structural Patterns: Organise the Chaos Think of this as the architecture layer. These patterns help you compose and structure code efficiently. 💡 Use these when: You’re bridging mismatched interfaces (Adapter) You want to wrap and enhance existing objects (Decorator) You need to simplify a complex system into one entry point (Facade) You’re building object trees (Composite) You want memory optimization (Flyweight) You want to control access and protection (Proxy, Bridge) 🔷 Behavioural Patterns: Handle Interactions & Responsibilities These deal with how objects interact and share responsibilities. It’s about communication, delegation, and dynamic behavior. 💡 Use these when: You want to notify multiple observers of changes (Observer) You’re navigating through collections (Iterator) You want to encapsulate operations or algorithms (Command, Strategy) You need undo/redo functionality (Memento) You need to manage state transitions (State) You’re passing tasks down a chain (Chain of Responsibility) 📌 Whether you're preparing for interviews or trying to scale your application, understanding these 3 categories is a must: 🔹 Creational → Creating Objects 🔹 Structural → Assembling Objects 🔹 Behavioral → Object Interaction & Responsibilities Mastering these gives you a mental map to write scalable, reusable, and testable code. It’s not about memorising them, it's about knowing when and why to use them. #softwareengineering #systemdesign #linkedintech #sde #connections #networking LinkedIn LinkedIn News India

Most people don’t fail in DSA because it’s hard. They fail because they try to learn everything instead of learning the right patterns. If you’re a fresher preparing for coding interviews, stop collecting questions. Start mastering patterns. Here’s the exact roadmap I recommend 👇 1️⃣ Arrays Core patterns you must know: • Two Pointers • Sliding Window (fixed and variable) • Prefix Sum • Kadane’s Algorithm • Hashing / Frequency Map • Sorting + Greedy • Cyclic Sort • Binary Search 2️⃣ Linked Lists Core patterns: • Fast & Slow Pointer • Dummy Node • Reversal (entire list / k-group) • Merge Lists • Pointer Rewiring 3️⃣ Stack & Queue Core patterns: • Monotonic Stack • Monotonic Queue • Stack for Previous / Next Greater • Sliding Window + Deque 4️⃣ Trees & Graphs Core patterns: • DFS (pre / in / post order) • BFS (level order) • Recursion • Backtracking on Trees • Dijkstra • Topological Sort • Union Find 5️⃣ Advanced Patterns • Binary Search on Answer • Greedy • Dynamic Programming ◦ 0/1 Knapsack ◦ Unbounded Knapsack ◦ DP on Strings • Heap (Top K, Merge K) • Bit Manipulation You don’t need 1000 problems. You need clarity on these patterns. Once you understand the pattern, 10 different questions start looking the same. That’s when preparation becomes smart. If you’re preparing for placements or switching jobs, save this post and follow for more such content ❤️

Top 5 Must-Know DSA Patterns👇🏻👇🏻 DSA problems often follow recurring patterns. Mastering these patterns can make problem-solving more efficient and help you ace coding interviews. Here’s a quick breakdown: 1. Sliding Window • Use Case: Solves problems involving contiguous subarrays or substrings. • Key Idea: Slide a window over the data to dynamically track subsets. • Examples: • Maximum sum of subarray of size k. • Longest substring without repeating characters. 2. Two Pointers • Use Case: Optimizes array problems involving pairs or triplets of elements. • Key Idea: Use two pointers to traverse from opposite ends or incrementally. • Examples: • Pair with target sum in a sorted array. • Trapping rainwater problem. 3. Binary Search • Use Case: Efficiently solves problems with sorted data or requiring optimization. • Key Idea: Repeatedly halve the search space to narrow down the solution. • Examples: • Find an element in a sorted array. • Search in a rotated sorted array. 4. Dynamic Programming (DP) • Use Case: Handles problems with overlapping subproblems and optimal substructure. • Key Idea: Build solutions iteratively using a table to store intermediate results. • Examples: • 0/1 Knapsack problem. • Longest common subsequence. 5. Backtracking • Use Case: Solves problems involving all possible combinations, subsets, or arrangements. • Key Idea: Incrementally build solutions and backtrack when a condition is not met. • Examples: • N-Queens problem. • Sudoku solver. Why These Patterns? By focusing on patterns, you can identify the right approach quickly, saving time and improving efficiency in problem-solving.

I analyzed the top 50 coding interview questions, and they all boil down to these 18 patterns. People ask me how to crack technical interviews without spending years on LeetCode. My secret? I don't memorize solutions. People ask how I identify the right approach for a brand new problem instantly. My secret? I look for the underlying pattern, not the specific question. But the truth is... There is no secret. Just pure Pattern Recognition. To master DSA, you have to stop treating every problem as unique. You need to map them to these 18 fundamental branches. Here is the technical breakdown to get you started: 1. Optimization & Pointers - Two Pointers: Essential for sorted arrays and linked lists. Use this to detect cycles (Floyd's algorithm), remove elements, or find target pairs in O(N) time. - Sliding Window: The standard for subarray problems. Perfect for calculating running averages, finding the longest substring under constraints, or optimization within a linear data structure. - Intervals: When dealing with time ranges or overlaps, use Merge Intervals or Catalan logic. 2. Search & Traversal - Binary Search: Beyond finding numbers. Use on rotated sorted arrays or to find "first/last occurrence" boundaries in O(log N). - Tree Traversal: Master the recursion. Know when to use Level-order (BFS) vs. Pre/In/Post-order (DFS) for tasks like serialization or finding the Lowest Common Ancestor. - Graph Traversal: Solves island counting, cycle detection, and topological sorting. 3. Complex Structures & Logic - Heaps: The most efficient way to handle "Top K" elements, scheduling tasks, or finding medians in a data stream. - Tries: The go-to design pattern for autocomplete systems, spell checkers, and prefix searches. - Backtracking: For when you need all possibilities. Used in generating permutations, N-Queens, and Sudoku solvers. 4. The Heavy Hitters - Dynamic Programming (DP): For overlapping subproblems. Includes 1D/2D arrays, Longest Common Subsequence (LCS), and the Knapsack problem. - Graph Optimization (Union Find): Critical for network connectivity. Uses Disjoint Set Union and MST algorithms like Kruskal’s or Prim’s. Want to be a software engineer? Stop memorizing. Start recognizing. Remember, seeing the pattern is 90% of the solution. The code is just syntax. Which of these patterns do you find most difficult to implement? ♻️ Repost to help a connection ace their technical interview.

Master these strategies to write clean, reusable code across all data roles. Here is how you keep your code clean, efficient, and adaptable:  1. 𝗠𝗼𝗱𝘂𝗹𝗮𝗿 𝗗𝗲𝘀𝗶𝗴𝗻: Break down your code into distinct functions that handle individual tasks. This modular approach allows you to reuse functions across different projects and makes debugging far easier.       2. 𝗗𝗼𝗰𝘂𝗺𝗲𝗻𝘁𝗮𝘁𝗶𝗼𝗻: Comment your code clearly and provide README files for larger projects. Explain what your functions do, the inputs they accept, and the expected outputs. This makes onboarding new team members smoother and helps your future self understand the logic quickly.       3. 𝗣𝗮𝗿𝗮𝗺𝗲𝘁𝗲𝗿𝗶𝘇𝗮𝘁𝗶𝗼𝗻: Use parameters for values that could change over time, such as file paths, column names, or thresholds. This flexibility ensures that your code is adaptable without requiring major rewrites.       4. 𝗜𝗻𝘁𝗲𝗻𝘁𝗶𝗼𝗻𝗮𝗹 𝗡𝗮𝗺𝗶𝗻𝗴: Variable, function, and class names are your first layer of documentation. Make them descriptive and consistent.       5. 𝗖𝗼𝗻𝘀𝗶𝘀𝘁𝗲𝗻𝘁 𝗦𝘁𝘆𝗹𝗲: Adopt a coding standard and stick to it. Whether it’s the way you format loops or how you organize modules, consistency makes your code predictable and easier to follow.       6. 𝗘𝗿𝗿𝗼𝗿 𝗛𝗮𝗻𝗱𝗹𝗶𝗻𝗴: Include error handling in your functions. Use try-except blocks to catch exceptions, and provide informative messages that indicate what went wrong and how to fix it.       7. 𝗧𝗲𝘀𝘁𝗶𝗻𝗴: Implement unit tests to verify that each function performs as expected. This proactive approach helps identify issues early and ensures that changes don’t introduce new bugs.       8. 𝗩𝗲𝗿𝘀𝗶𝗼𝗻 𝗖𝗼𝗻𝘁𝗿𝗼𝗹: Use Git or another version control system to manage changes to your code. It allows you to track progress, roll back mistakes, and collaborate seamlessly.       9. 𝗖𝗼𝗱𝗲 𝗥𝗲𝘃𝗶𝗲𝘄𝘀: Encourage peer reviews to catch potential issues, share best practices, and foster a culture of collaborative learning.      10. 𝗥𝗲𝘃𝗶𝗲𝘄 𝗮𝗻𝗱 𝗥𝗲𝗳𝗮𝗰𝘁𝗼𝗿: Review your code after a break, seeking opportunities to simplify and improve. Refactoring is your path to more robust and efficient code.   Whether writing small SQL queries or building large Python models, a clean coding style will make you a more efficient analyst. It’s an investment that will pay off in productivity and reliability. What’s your top tip for writing reusable code? ---------------- ♻️ Share if you find this post useful ➕ Follow for more daily insights on how to grow your career in the data field #dataanalytics #datascience #python #cleancode #productivity

The Case of the Costly Error Once upon a time, a critical bug in a bustling software company was reported in their flagship product just days before a major release. Panic spread through the team like wildfire. The bug was complex, and time was running out. At first, the team tried the usual approach—frantic debugging and patching. But the bug kept reappearing like a stubborn ghost. As deadlines loomed closer, frustration mounted. That's when Jane, one of the senior developers, stepped in. She suggested a different approach: structured problem-solving. She gathered the team in a meeting room and laid out a plan: 01. Define the Problem: They dissected the bug, identified its specific behaviors, and defined the problem statement clearly. 02. Collect Data: They gathered data on when the bug occurred, what actions triggered it, and the system conditions at that moment. 03. Generate Hypotheses: The team brainstormed potential causes, generating multiple hypotheses. 04. Test Hypotheses: They systematically tested each hypothesis individually, isolating variables and gathering more data. 05. Analyze Results: Based on the data collected, they analyzed the results of each test and eliminated hypotheses that didn't hold up. 06. Implement Solution: Finally, they identified the root cause and implemented a solution that fixed the bug once and for all. The bug was squashed, and the release went off without a hitch. What could have been a disaster turned into a valuable lesson. Structured problem-solving saved the day! → When faced with a daunting challenge, don't rush into solutions. Take a structured approach. #dhandhekafunda ps: Structured problem-solving approach acts as a compass when you are not emotionally trapped in the situation. If you are, have another competent individual take the lead. At least be that structured ;)

In 2021, I failed my leetcode interviews at Amazon. Today, I conduct technical interviews at AWS. Back then, leetcode felt overwhelming. I remember staring at problems for hours wondering if I’d ever get it. I jumped between arrays, graphs and dynamic programming — hoping something would click. But it didn’t. And solving 3500+ leetcode problems felt impossible. Then I realised something that changed everything: It’s not about solving thousands of problems. It’s about learning the patterns behind them. Once I focused on the core DSA patterns everything started to make sense. Here are the patterns that cover most interview questions: 1. Two Pointers ↳ Used for sorted arrays & strings (pair sum, removing duplicates, merging in place). 2. Fast & Slow Pointers ↳ Cycle detection, middle of linked list, detecting starting point of cycle. 3. Sliding Window ↳ Longest / shortest subarray or substring under constraints (k-distinct, frequency limits). 4. Prefix Sum ↳ Subarray sums, range queries, difference arrays. 5. Monotonic Stack / Queue ↳ Next greatest element, stock span, daily temperatures, sliding window max 6. Merge Intervals ↳ Overlapping intervals, meeting rooms, merging ranges. 7. Sorting + Sweep Line ↳ Event processing, scheduling, interval counting, greedy decisions. 8. Divide & Conquer ↳ Merge sort, quicksort, finding medians, recursive splitting. 9. Binary Search (All Variants) ↳ Sorted arrays, rotated arrays, “search on answer” for thresholds or minima. 10. Greedy Algorithms ↳ Activity selection, gas station, optimal scheduling & choice making. 11. Linked List Techniques ↳ Reversal, merging, reordering 12. Heaps & Top-K ↳ Priority queues, top-k elements, streaming median, smallest/largest k. 13. Hashmaps & Frequency Counting ↳ Anagrams, duplicates, sliding window character maps. 14. Dynamic Programming ↳ 1D/2D DP, subsequences, knapsack, DP on strings. 15. Backtracking / Recursive Search ↳ Permutations, subsets, combinations, N-Queens, search trees. 16. Graph Traversals (BFS & DFS) ↳ Connected components, islands, shortest path (unweighted), cycle detection. 17. Topological Sort (DAG Ordering) ↳ Course schedule, dependency resolution, task ordering. 18. Binary Tree Traversals (DFS/BFS) ↳ Preorder, inorder, postorder, level order traversal patterns. 19. Tree Path Problems ↳ Root-to-leaf sums, path sum, DFS with backtracking. 20. Trie (Prefix Tree) ↳ Autocomplete, prefix matching, dictionary search, word problems. Once you understand these patterns, leetcode starts to make a lot more sense. If you’re starting today: → Learn core DSA: arrays, hashmaps, stacks, queues, linked lists, graphs and trees. → Tackle one pattern at a time. Do 2–4 problems per pattern. → Create a study plan & revisit old problems as you learn new ones. → When ready, take on Blind75 questions. Save this for your next interview. Follow Abdirahman Jama for more practical software engineering tips. #softwareengineering

I’ve reviewed close to 2000+ code review requests in my career. At this point, it’s as natural to me as having a cup of coffee. However, from a senior engineer to now an engineering manager, I’ve learned a lot in between. If I had to learn to review code all over again, this would be the checklist I follow (inspired from my experience) 1. Ask clarifying questions:      - What are the exact constraints or edge cases I should consider?      - Are there any specific inputs or outputs to watch for?      - What assumptions can I make about the data?      - Should I optimize for time or space complexity?  2. Start simple:      - What is the most straightforward way to approach this?      - Can I explain my initial idea in one sentence?      - Is this solution valid for the most common cases?      - What would I improve after getting a basic version working?  3. Think out loud:      - Why am I taking this approach over another?      - What trade-offs am I considering as I proceed?      - Does my reasoning make sense to someone unfamiliar with the problem?      - Am I explaining my thought process clearly and concisely?  4. Break the problem into smaller parts:      - Can I split the problem into logical steps?      - What sub-problems need solving first?      - Are any of these steps reusable for other parts of the solution?      - How can I test each step independently?  5. Use test cases:      - What edge cases should I test?      - Is there a test case that might break my solution?      - Have I checked against the sample inputs provided?      - Can I write a test to validate the most complex scenario?  6. Handle mistakes gracefully:      - What’s the root cause of this mistake?      - How can I fix it without disrupting the rest of my code?      - Can I explain what went wrong to the interviewer?      - Did I learn something I can apply to the rest of the problem?  7. Stick to what you know:      - Which language am I most confident using?      - What’s the fastest way I can implement the solution with my current skills?      - Are there any features of this language that simplify the problem?      - Can I use familiar libraries or tools to save time?  8. Write clean, readable code:      - Is my code easy to read and understand?      - Did I name variables and functions meaningfully?      - Does the structure reflect the logic of the solution?      - Am I following best practices for indentation and formatting?  9. Ask for hints when needed:      - What part of the problem am I struggling to understand?      - Can the interviewer provide clarification or a nudge?      - Am I overthinking this?      - Does the interviewer expect a specific approach?  10. Stay calm under pressure:      - What’s the first logical step I can take to move forward?      - Have I taken a moment to reset my thoughts?      - Am I focusing on the problem, not the time ticking away?      - How can I reframe the problem to make it simpler?