Top 10 Must-Know Coding Concepts every interviewer expects you to know.

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*1. Arrays & Strings – The Basics That Build Everything*

Arrays are ordered collections. Strings are just arrays of characters.

You’ll use them in 90% of coding problems.

Beginner Example: Find the max number in an array, reverse a string, check if it’s a palindrome.

Start with: Leetcode Easy Array Problems


*2. Hashing – Remember Stuff Fast*

What it is: Like a super-efficient locker room. You store and find things instantly using keys.

Real Use-case: Count frequencies, detect duplicates, group similar data.

Example: Check if two strings are anagrams.

Use: HashMap or Dictionary in Python


*3. Recursion – When Functions Call Themselves*

What it is: A function solving a smaller version of the same problem.

Looks Scary? It’s not. Think of solving a puzzle by solving one piece at a time.

Example: Factorial, Fibonacci numbers.

Golden Rule: Always define a base case, or it loops forever!


*4. Backtracking – Trial & Error, Smartly Done*

What it is: Try all possible options, but drop paths that don’t work early.

Real World Analogy: Like navigating a maze – go back if you hit a wall.

Example: Sudoku Solver, N-Queens Problem


*5. Dynamic Programming (DP) – Avoid Repeating Work*

What it is: Break problems into smaller parts and store the result so you don’t repeat it.

Example: Fibonacci using DP instead of recursion (faster!)


*6. Sliding Window – Efficient Way to Check Patterns in a Row*

What it is: Instead of checking every combination, move a “window” across the array to find answers.

Example: Find max sum of subarray of size K.

Great for string and array problems.


*7. Trees – Hierarchical Data You Must Understand*

What it is: Like a family tree. Each node can have children.

Key Terms: Root, Leaf, Binary Tree, BST

Why it’s asked: Real apps like file systems, websites use trees.

Example: Inorder/Preorder/Postorder Traversals


*8. Graphs – Networks of Connections*

What it is: Nodes connected by edges. Can go in any direction.

Examples: Maps, social media friends, recommendation engines

Learn: BFS (Breadth-First Search), DFS (Depth-First Search)


*9. Greedy – Pick Best at Every Step (Fast but Risky)*

What it is: Make the best local choice hoping it leads to the global best.

Good For Simple optimization problems

Example: Activity Selection, Coin Change (with greedy strategy)


*10. Bit Manipulation – Play with 0s and 1s*

What it is: Perform operations directly on binary representations. It’s super fast and memory-efficient

Example: Check if a number is a power of 2, find the only non-repeating element


What to Do Next (Action Plan):

- Start with Arrays, then move to Hashing

- Try Recursion + Backtracking next

- Once comfy, go into DP, Graphs, and Trees

- Use platforms like Leetcode (easy → medium), GeeksforGeeks, or Neetcode

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Programming Resources: 👇 https://whatsapp.com/channel/0029VahiFZQ4o7qN54LTzB17