Coding Interview Resources
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This channel contains the free resources and solution of coding problems which are usually asked in the interviews.

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โœ… ๐Ÿ”ค Aโ€“Z of Programming ๐Ÿ’ป

A โ€“ API (Application Programming Interface)
Interface for programs to communicate with each other.

B โ€“ Bug
Error or flaw in a program that causes incorrect results.

C โ€“ Compiler
Tool that converts code into executable machine language.

D โ€“ Debugging
Process of finding and fixing bugs in code.

E โ€“ Exception
An error detected during execution, often requiring handling.

F โ€“ Function
Reusable block of code that performs a specific task.

G โ€“ Git
Version control system for tracking code changes.

H โ€“ HTML (HyperText Markup Language)
Standard language for building web pages.

I โ€“ IDE (Integrated Development Environment)
Software that combines tools for coding, testing, and debugging.

J โ€“ JavaScript
Language for building interactive web applications.

K โ€“ Keyword
Reserved word with special meaning in a programming language.

L โ€“ Loop
Structure for repeating a block of code multiple times.

M โ€“ Module
File containing reusable code, functions, or classes.

N โ€“ Namespace
Container to organize identifiers and avoid naming conflicts.

O โ€“ Object-Oriented Programming (OOP)
Paradigm based on objects and classes to structure code.

P โ€“ Parameter
Value passed to a function to customize its behavior.

Q โ€“ Query
Instruction to retrieve data, often from databases.

R โ€“ Recursion
Function that calls itself to solve a problem.

S โ€“ Syntax
Rules that define how code must be written.

T โ€“ Try-Catch
Error-handling structure to catch exceptions.

U โ€“ UI (User Interface)
Part of the program users interact with visually.

V โ€“ Variable
Named storage for data in a program.

W โ€“ While Loop
Loop that continues as long as a condition is true.

X โ€“ XML
Markup language for storing and sharing structured data.

Y โ€“ YAML
Readable format used for config files in DevOps and backends.

Z โ€“ Zero-based Indexing
Common system where counting in arrays starts at 0.

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โœ… Coding Interview Questions with Answers [Part-1] ๐Ÿ’ป๐Ÿš€

1. What is the time and space complexity of your code?
Time complexity measures how the runtime grows with input size. Space complexity measures memory used. Always analyze both to optimize your solution.

2. What is the difference between an array and a linked list?
Arrays store elements contiguously with fast access by index. Linked lists store elements as nodes connected by pointers, allowing easy insertion/deletion but slower access.

3. How does a HashMap work internally?
It uses a hash function to convert keys into indexes in an array. Collisions are handled by chaining (linked lists) or open addressing.

4. What is recursion? Give an example.
Recursion is a function calling itself to solve smaller subproblems.
Example: Factorial(n) = n ร— Factorial(n-1), with base case Factorial(0) = 1.

5. Explain stack vs. queue.
Stack: Last In First Out (LIFO), like a stack of plates.
Queue: First In First Out (FIFO), like a line at a store.

6. What is a binary search and when to use it?
Binary search efficiently finds an item in a sorted array by repeatedly dividing the search interval in half. Use on sorted data for O(log n) time.

7. What is the difference between BFS and DFS?
BFS (Breadth-First Search) explores nodes level by level using a queue.
DFS (Depth-First Search) explores as far as possible along a branch using a stack or recursion.

8. What is dynamic programming?
A method to solve problems by breaking them into overlapping subproblems and storing solutions to avoid repeated work.

9. Solve Fibonacci using memoization.
Memoization stores already calculated Fibonacci numbers in a cache to reduce repeated calculations and improve performance from exponential to linear time.

10. Explain two-pointer technique with an example.
Use two pointers to traverse data structures simultaneously.
Example: Find if a sorted array has two numbers summing to a target by moving pointers from start and end inward.

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โœ… Coding Interview Questions with Answers [Part-2] ๐Ÿ’ป๐Ÿš€

11. What is a sliding window algorithm?
A technique for solving problems involving arrays or strings by maintaining a window that slides over data. It helps reduce time complexity by avoiding nested loops.
Example: Finding the max sum of subarrays of size k.

12. Detect cycle in a linked list.
Use Floyd's Cycle Detection Algorithm (Tortoise and Hare).
โฆ Move two pointers at different speeds.
โฆ If they meet, a cycle exists.
โฆ To find the cycle start, reset one pointer to head and move both one step until they meet again.

13. Find the intersection of two arrays.
Use a HashSet to store elements of the first array, then check each element in the second array.
โฆ Time: O(n + m)
โฆ Space: O(min(n, m))

14. Reverse a string or linked list.
โฆ For a string: Use two-pointer swap or Python's slicing.
โฆ For a linked list: Use three pointers (prev, curr, next) and iterate while reversing links.

15. Check if a string is a palindrome.
Use two pointers from start and end, compare characters.
Return false if mismatch, true if all characters match.

16. What are the different sorting algorithms?
โฆ Bubble Sort
โฆ Selection Sort
โฆ Insertion Sort
โฆ Merge Sort
โฆ Quick Sort
โฆ Heap Sort
โฆ Radix Sort
Each has different time and space complexities.

17. Explain quicksort vs. mergesort.
โฆ Quicksort: Divide and conquer, picks a pivot.
โฆ Average: O(n log n), Worst: O(nยฒ), Space: O(log n)
โฆ Mergesort: Always divides array into halves, then merges.
โฆ Time: O(n log n), Space: O(n), Stable sort

18. What is a binary search tree (BST)?
A tree where left child < node < right child.
โฆ Efficient for searching, insertion, deletion: O(log n) if balanced.
โฆ Unbalanced BST can degrade to O(n)

19. Inorder, Preorder, Postorder traversals.
โฆ Inorder (LNR): Sorted order in BST
โฆ Preorder (NLR): Used to copy or serialize tree
โฆ Postorder (LRN): Used to delete tree

20. Implement LRU Cache.
Use a combination of HashMap + Doubly Linked List.
โฆ HashMap stores key-node pairs.
โฆ Linked list maintains access order.
โฆ When cache is full, remove the least recently used node.
Operations (get, put): O(1) time.

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โœ… Coding Interview Questions with Answers [Part-3] ๐Ÿ’ป๐Ÿš€

21. Find the longest substring without repeating characters 
Use a sliding window with a set to track characters. 
def length_of_longest_substring(s):
    seen = set()
    left = max_len = 0
    for right in range(len(s)):
        while s[right] in seen:
            seen.remove(s[left])
            left += 1
        seen.add(s[right])
        max_len = max(max_len, right - left + 1)
    return max_len

22. Explain backtracking with N-Queens problem 
Backtracking tries placing a queen in each column, then recursively places the next queen if safe. If no safe position is found, it backtracks. 
def solve_n_queens(n):
    result = []
    board = [-1]ร—n

    def is_safe(row, col):
        for r in range(row):
            if board[r] == col or abs(board[r] - col) == abs(r - row):
                return False
        return True

    def backtrack(row=0):
        if row == n:
            result.append(board[:])
            return
        for col in range(n):
            if is_safe(row, col):
                board[row] = col
                backtrack(row + 1)
                board[row] = -1

    backtrack()
    return result

23. What is a trie? Where is it used?
A Trie is a tree-like data structure used for efficient retrieval of strings, especially for autocomplete or prefix matching. 
Used in: 
- Dictionary lookups 
- Search engines 
- IP routing

24. Explain bit manipulation tricks 
- Check if number is power of 2: n & (n - 1) == 0 
- Count set bits: bin(n).count('1') 
- Swap without temp: x = x ^ y; y = x ^ y; x = x ^ y

25. Kadaneโ€™s Algorithm for maximum subarray sum 
def max_subarray(nums):
    max_sum = current = nums[0]
    for num in nums[1:]:
        current = max(num, current + num)
        max_sum = max(max_sum, current)
    return max_sum

26. What are heaps and how do they work? 
Heap is a binary tree where parent is always smaller (min-heap) or larger (max-heap) than children. Supports O(log n) insert and delete. 
Use Pythonโ€™s heapq for min-heaps.

27. Find kth largest element in an array 
import heapq
def find_kth_largest(nums, k):
    return heapq.nlargest(k, nums)[-1]

28. How to detect cycle in a graph? 
Use DFS with visited and recursion stack. 
def has_cycle(graph):
    visited = set()
    rec_stack = set()

    def dfs(v):
        visited.add(v)
        rec_stack.add(v)
        for neighbor in graph[v]:
              if neighbor not in visited and dfs(neighbor):
                return True
            elif neighbor in rec_stack:
                return True
        rec_stack.remove(v)
        return False

    for node in graph:
        if node not in visited and dfs(node):
            return True
    return False


29. Topological sort of a DAG 
Used to sort tasks with dependencies. 

def topological_sort(graph):
    visited, result = set(), []

    def dfs(node):
        if node in visited:
            return
        visited.add(node)
        for neighbor in graph.get(node, []):
            dfs(neighbor)
        result.append(node)

    for node in graph:
        dfs(node)
    return result[::-1]


30. Implement a stack using queues 

from collections import deque

class Stack:
    def init(self):
        self.q = deque()

    def push(self, x):
        self.q.append(x)
        for _ in range(len(self.q) - 1):
            self.q.append(self.q.popleft())

    def pop(self):
        return self.q.popleft()

    def top(self):
        return self.q[0]

    def empty(self):
        return not self.q


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โœ… DSA Roadmap for Beginners (2025) ๐Ÿ”ข๐Ÿง 

1. Understand What DSA Is
โฆ Data Structures organize data efficiently; Algorithms solve problems step-by-step
โฆ Why learn: Boosts coding interviews, optimizes code for tech jobs

2. Pick a Programming Language
โฆ Start with Python, C++, or Java for syntax basics
โฆ Focus on loops, arrays, functions before diving deep

3. Learn Time & Space Complexity
โฆ Big-O notation: O(1), O(n), O(nยฒ)
โฆ Analyze efficiency to write better code

4. Master Basic Data Structures
โฆ Arrays & Strings: Indexing, manipulation
โฆ Linked Lists: Insertion, deletion, reversal

5. Explore Stacks & Queues
โฆ LIFO (Stack) for undo operations, FIFO (Queue) for tasks
โฆ Applications: Parentheses balancing, BFS

6. Dive into Trees & Graphs
โฆ Binary Trees, BSTs: Traversal (BFS/DFS)
โฆ Graphs: Adjacency lists, shortest paths (Dijkstra)

7. Learn Sorting & Searching
โฆ Algorithms: Bubble, Merge, Quick Sort; Binary Search
โฆ Understand when to use each for efficiency

8. Tackle Recursion & Backtracking
โฆ Base cases, recursive calls
โฆ Problems: Subsets, N-Queens

9. Work on Dynamic Programming
โฆ Memoization, tabulation
โฆ Classics: Fibonacci, Knapsack, LCS

10. Bonus Skills
โฆ Heaps, Tries, Greedy algorithms
โฆ Practice on LeetCode, HackerRank; build projects like pathfinders

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โœ… JavaScript Essentials โ€“ Interview Questions with Answers ๐Ÿง ๐Ÿ’ป

1๏ธโƒฃ Q: What is the difference between let, const, and var?
A:
โฆ var: Function-scoped, hoisted, can be redeclared.
โฆ let: Block-scoped, not hoisted like var, can't be redeclared in same scope.
โฆ const: Block-scoped, must be assigned at declaration, cannot be reassigned.

2๏ธโƒฃ Q: What are JavaScript data types?
A:
โฆ Primitive types: string, number, boolean, null, undefined, symbol, bigint
โฆ Non-primitive: object, array, function
Type coercion: JS automatically converts between types in operations ('5' + 2 โ†’ '52')

3๏ธโƒฃ Q: How does DOM Manipulation work in JS?
A:
The DOM (Document Object Model) represents the HTML structure. JS can access and change elements using:
โฆ document.getElementById()
โฆ document.querySelector()
โฆ element.innerHTML (sets HTML content), element.textContent (sets text only), element.style (applies CSS)
Example: document.querySelector('p').textContent = 'Updated text!';

4๏ธโƒฃ Q: What is event handling in JavaScript?
A:
It allows reacting to user actions like clicks or key presses.
Example:
document.getElementById("btn").addEventListener("click", () => {
alert("Button clicked!");
});


5๏ธโƒฃ Q: What are arrow functions?
A:
A shorter syntax for functions introduced in ES6.
const add = (a, b) => a + b;


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๐Ÿ‘จโ€๐ŸŽ“System Design Topics: Cheat Sheet for Interview Preparation

โ˜‘๏ธ Load Balancing
โ˜‘๏ธ API Gateway
โ˜‘๏ธ Communication Protocols
โ˜‘๏ธ CDN (Content Delivery Network)
โ˜‘๏ธ Database
โ˜‘๏ธ Cache
โ˜‘๏ธ Message Queue
โ˜‘๏ธ Generating Unique Identifiers
โ˜‘๏ธ Scalability
โ˜‘๏ธ Availability
โ˜‘๏ธ Performance
โ˜‘๏ธ Fault Tolerance and Recovery
โ˜‘๏ธ Security and much more
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โœ… Programming Language Fun Facts ๐Ÿง ๐Ÿ’ป

1๏ธโƒฃ Python ๐Ÿ
โฆ Created by Guido van Rossum in 1991
โฆ Known for readability and simplicity
โฆ Tops 2025 charts in AI, data science, and automation

2๏ธโƒฃ JavaScript ๐ŸŒ
โฆ Invented in just 10 days by Brendan Eich (1995)
โฆ Runs in every modern web browser
โฆ Powers 95%+ of websites

3๏ธโƒฃ C ๐Ÿ–ฅ๏ธ
โฆ Developed by Dennis Ritchie between 1969-73
โฆ Backbone of OS kernels and embedded systems
โฆ Foundation for C++, C#, Objective-C

4๏ธโƒฃ Java โ˜•
โฆ Released by Sun Microsystems in 1995
โฆ โ€œWrite once, run anywhereโ€ mantra
โฆ Powers Android apps and enterprise software

5๏ธโƒฃ Rust ๐Ÿฆ€
โฆ Launched by Mozilla in 2010
โฆ Focuses on memory safety without a garbage collector
โฆ Popular for system-level programming

6๏ธโƒฃ Go (Golang) ๐Ÿน
โฆ Created at Google in 2009
โฆ Designed for simplicity and performance
โฆ Great for backend and microservices

7๏ธโƒฃ TypeScript ๐Ÿ”ท
โฆ Microsoftโ€™s superset of JavaScript (2012)
โฆ Adds static typing
โฆ Hot in large frontend projects

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