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Coding interview questions with concise answers for software roles:
1๏ธโฃ What happens when you type a URL and hit Enter?
Answer:
- DNS Lookup โ IP address
- Browser sends HTTP/HTTPS request
- Server responds with HTML/CSS/JS
- Browser builds DOM, applies styles (CSSOM), runs JS
- Page is rendered
2๏ธโฃ Difference between var, let, and const?
Answer:
- var: function-scoped, hoisted
- let: block-scoped, not hoisted
- const: block-scoped, canโt be reassigned
3๏ธโฃ Reverse a String in JavaScript
Answer:
A function that remembers variables from its outer scope even after the outer function has returned.
7๏ธโฃ What is event delegation?
Answer:
Attaching a single event listener to a parent element to manage events on its children using
8๏ธโฃ Difference between == and ===
Answer:
- == checks value (with type coercion)
- === checks value + type (strict comparison)
9๏ธโฃ What is the Virtual DOM?
Answer:
A lightweight copy of the real DOM used in React. React updates the virtual DOM first and then applies only the changes to the real DOM for efficiency.
๐ Write code to remove duplicates from an array
1๏ธโฃ What happens when you type a URL and hit Enter?
Answer:
- DNS Lookup โ IP address
- Browser sends HTTP/HTTPS request
- Server responds with HTML/CSS/JS
- Browser builds DOM, applies styles (CSSOM), runs JS
- Page is rendered
2๏ธโฃ Difference between var, let, and const?
Answer:
- var: function-scoped, hoisted
- let: block-scoped, not hoisted
- const: block-scoped, canโt be reassigned
3๏ธโฃ Reverse a String in JavaScript
function reverseString(str) {
return str.split('').reverse().join('');
}
4๏ธโฃ Find the max number in an arrayconst max = Math.max(...arr);5๏ธโฃ Write a function to check if a number is prime
function isPrime(n) {
if (n < 2) return false;
for (let i = 2; i <= Math.sqrt(n); i++) {
if (n % i === 0) return false;
}
return true;
}
6๏ธโฃ What is closure in JavaScript? Answer:
A function that remembers variables from its outer scope even after the outer function has returned.
7๏ธโฃ What is event delegation?
Answer:
Attaching a single event listener to a parent element to manage events on its children using
event.target.8๏ธโฃ Difference between == and ===
Answer:
- == checks value (with type coercion)
- === checks value + type (strict comparison)
9๏ธโฃ What is the Virtual DOM?
Answer:
A lightweight copy of the real DOM used in React. React updates the virtual DOM first and then applies only the changes to the real DOM for efficiency.
๐ Write code to remove duplicates from an array
const uniqueArr = [...new Set(arr)];React โค๏ธ for more
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10 Key Programming Differences! ๐ป๐
1๏ธโฃ Python 2 vs Python 3
โก๏ธ Python 2: Legacy, no updates
โก๏ธ Python 3: Modern, better syntax support
๐ Always use Python 3 for new projects.
2๏ธโฃ Static vs Dynamic Typing
โก๏ธ Static: Type declared (e.g., Java, C++)
โก๏ธ Dynamic: Type inferred at runtime (e.g., Python, JavaScript)
๐ Static = fewer bugs, Dynamic = faster dev
3๏ธโฃ Abstraction vs Encapsulation
โก๏ธ Abstraction: Hides complexity
โก๏ธ Encapsulation: Hides data
๐ Abstraction = "What", Encapsulation = "How"
4๏ธโฃ REST vs SOAP (APIs)
โก๏ธ REST: Lightweight, uses HTTP
โก๏ธ SOAP: Protocol, strict rules
๐ REST is more common today
5๏ธโฃ SQL vs NoSQL
โก๏ธ SQL: Structured data, tables (e.g., MySQL)
โก๏ธ NoSQL: Unstructured, scalable (e.g., MongoDB)
๐ SQL = Relational, NoSQL = Flexible
6๏ธโฃ For Loop vs While Loop
โก๏ธ For: Known iterations
โก๏ธ While: Unknown, condition-based
๐ Use for when count is known.
7๏ธโฃ Function vs Method
โก๏ธ Function: Independent block
โก๏ธ Method: Function inside class
๐ All methods are functions, not vice versa
8๏ธโฃ Frontend vs Backend
โก๏ธ Frontend: User interface (HTML, CSS, JS)
โก๏ธ Backend: Server logic, DB (Node.js, Python, etc.)
๐ Frontend = what users see
9๏ธโฃ Procedural vs OOP
โก๏ธ Procedural: Functions logic
โก๏ธ OOP: Objects, classes
๐ OOP = more modular reusable
๐ Null vs Undefined (JavaScript)
โก๏ธ Null: Assigned empty value
โก๏ธ Undefined: Variable declared, not assigned
๐ typeof null is 'object', quirky but true!
๐ฌ Tap โค๏ธ if you found this helpful!
1๏ธโฃ Python 2 vs Python 3
โก๏ธ Python 2: Legacy, no updates
โก๏ธ Python 3: Modern, better syntax support
๐ Always use Python 3 for new projects.
2๏ธโฃ Static vs Dynamic Typing
โก๏ธ Static: Type declared (e.g., Java, C++)
โก๏ธ Dynamic: Type inferred at runtime (e.g., Python, JavaScript)
๐ Static = fewer bugs, Dynamic = faster dev
3๏ธโฃ Abstraction vs Encapsulation
โก๏ธ Abstraction: Hides complexity
โก๏ธ Encapsulation: Hides data
๐ Abstraction = "What", Encapsulation = "How"
4๏ธโฃ REST vs SOAP (APIs)
โก๏ธ REST: Lightweight, uses HTTP
โก๏ธ SOAP: Protocol, strict rules
๐ REST is more common today
5๏ธโฃ SQL vs NoSQL
โก๏ธ SQL: Structured data, tables (e.g., MySQL)
โก๏ธ NoSQL: Unstructured, scalable (e.g., MongoDB)
๐ SQL = Relational, NoSQL = Flexible
6๏ธโฃ For Loop vs While Loop
โก๏ธ For: Known iterations
โก๏ธ While: Unknown, condition-based
๐ Use for when count is known.
7๏ธโฃ Function vs Method
โก๏ธ Function: Independent block
โก๏ธ Method: Function inside class
๐ All methods are functions, not vice versa
8๏ธโฃ Frontend vs Backend
โก๏ธ Frontend: User interface (HTML, CSS, JS)
โก๏ธ Backend: Server logic, DB (Node.js, Python, etc.)
๐ Frontend = what users see
9๏ธโฃ Procedural vs OOP
โก๏ธ Procedural: Functions logic
โก๏ธ OOP: Objects, classes
๐ OOP = more modular reusable
๐ Null vs Undefined (JavaScript)
โก๏ธ Null: Assigned empty value
โก๏ธ Undefined: Variable declared, not assigned
๐ typeof null is 'object', quirky but true!
๐ฌ Tap โค๏ธ if you found this helpful!
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โ
Core Data Structures Part 2 โ Stacks Queues ๐๐ฅ๐ค
Stacks and queues are fundamental linear data structures used in many algorithms and real-world applications like undo operations, task scheduling, and more.
1๏ธโฃ What is a Stack?
A Stack is a Last-In-First-Out (LIFO) structure.
Think of a stack of plates: you add (push) and remove (pop) from the top.
Operations:
โข push(item) โ Add item to the top
โข pop() โ Remove item from the top
โข peek() โ View top item without removing
โข is_empty() โ Check if stack is empty
Python Implementation (Using List)
2๏ธโฃ What is a Queue?
A Queue is a First-In-First-Out (FIFO) structure.
Think of a line at a ticket counter: first come, first served.
Operations:
โข enqueue(item) โ Add item to the rear
โข dequeue() โ Remove item from the front
โข peek() โ View front item
โข is_empty() โ Check if queue is empty
Python Implementation (Using collections.deque)
3๏ธโฃ Stack Using Linked List (Python)
4๏ธโฃ Queue Using Linked List (Python)
๐ Practice Tasks
1. Implement a stack using a list
2. Implement a queue using a list
3. Reverse a string using a stack
4. Check for balanced parentheses using a stack
5. Simulate a queue using two stacks
Double Tap โฅ๏ธ For More
Stacks and queues are fundamental linear data structures used in many algorithms and real-world applications like undo operations, task scheduling, and more.
1๏ธโฃ What is a Stack?
A Stack is a Last-In-First-Out (LIFO) structure.
Think of a stack of plates: you add (push) and remove (pop) from the top.
Operations:
โข push(item) โ Add item to the top
โข pop() โ Remove item from the top
โข peek() โ View top item without removing
โข is_empty() โ Check if stack is empty
Python Implementation (Using List)
stack = []
# Push
stack.append(10)
stack.append(20)
# Pop
print(stack.pop()) # 20
# Peek
print(stack[-1]) # 10
# Check empty
print(len(stack) == 0)
2๏ธโฃ What is a Queue?
A Queue is a First-In-First-Out (FIFO) structure.
Think of a line at a ticket counter: first come, first served.
Operations:
โข enqueue(item) โ Add item to the rear
โข dequeue() โ Remove item from the front
โข peek() โ View front item
โข is_empty() โ Check if queue is empty
Python Implementation (Using collections.deque)
from collections import deque
queue = deque()
# Enqueue
queue.append(10)
queue.append(20)
# Dequeue
print(queue.popleft()) # 10
# Peek
print(queue[0]) # 20
# Check empty
print(len(queue) == 0)
3๏ธโฃ Stack Using Linked List (Python)
class Node:
def __init__(self, data):
self.data = data
self.next = None
class Stack:
def __init__(self):
self.top = None
def push(self, data):
node = Node(data)
node.next = self.top
self.top = node
def pop(self):
if not self.top:
return None
data = self.top.data
self.top = self.top.next
return data
4๏ธโฃ Queue Using Linked List (Python)
class Node:
def __init__(self, data):
self.data = data
self.next = None
class Queue:
def __init__(self):
self.front = self.rear = None
def enqueue(self, data):
node = Node(data)
if not self.rear:
self.front = self.rear = node
else:
self.rear.next = node
self.rear = node
def dequeue(self):
if not self.front:
return None
data = self.front.data
self.front = self.front.next
if not self.front:
self.rear = None
return data
๐ Practice Tasks
1. Implement a stack using a list
2. Implement a queue using a list
3. Reverse a string using a stack
4. Check for balanced parentheses using a stack
5. Simulate a queue using two stacks
Double Tap โฅ๏ธ For More
โค4
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๐ฑ ๐๐ผ๐ฑ๐ถ๐ป๐ด ๐๐ต๐ฎ๐น๐น๐ฒ๐ป๐ด๐ฒ๐ ๐ง๐ต๐ฎ๐ ๐๐ฐ๐๐๐ฎ๐น๐น๐ ๐ ๐ฎ๐๐๐ฒ๐ฟ ๐๐ผ๐ฟ ๐๐ฎ๐๐ฎ ๐ฆ๐ฐ๐ถ๐ฒ๐ป๐๐ถ๐๐๐ ๐ป
You donโt need to be a LeetCode grandmaster.
But data science interviews still test your problem-solving mindsetโand these 5 types of challenges are the ones that actually matter.
Hereโs what to focus on (with examples) ๐
๐น 1. String Manipulation (Common in Data Cleaning)
โ Parse messy columns (e.g., split โName_Age_Cityโ)
โ Regex to extract phone numbers, emails, URLs
โ Remove stopwords or HTML tags in text data
Example: Clean up a scraped dataset from LinkedIn bias
๐น 2. GroupBy and Aggregation with Pandas
โ Group sales data by product/region
โ Calculate avg, sum, count using .groupby()
โ Handle missing values smartly
Example: โWhatโs the top-selling product in each region?โ
๐น 3. SQL Join + Window Functions
โ INNER JOIN, LEFT JOIN to merge tables
โ ROW_NUMBER(), RANK(), LEAD(), LAG() for trends
โ Use CTEs to break complex queries
Example: โGet 2nd highest salary in each departmentโ
๐น 4. Data Structures: Lists, Dicts, Sets in Python
โ Use dictionaries to map, filter, and count
โ Remove duplicates with sets
โ List comprehensions for clean solutions
Example: โCount frequency of hashtags in tweetsโ
๐น 5. Basic Algorithms (Not DP or Graphs)
โ Sliding window for moving averages
โ Two pointers for duplicate detection
โ Binary search in sorted arrays
Example: โDetect if a pair of values sum to 100โ
๐ฏ Tip: Practice challenges that feel like real-world data work, not textbook CS exams.
Use platforms like:
StrataScratch
Hackerrank (SQL + Python)
Kaggle Code
I have curated the best interview resources to crack Data Science Interviews
๐๐
https://whatsapp.com/channel/0029Va8v3eo1NCrQfGMseL2D
Like if you need similar content ๐๐
You donโt need to be a LeetCode grandmaster.
But data science interviews still test your problem-solving mindsetโand these 5 types of challenges are the ones that actually matter.
Hereโs what to focus on (with examples) ๐
๐น 1. String Manipulation (Common in Data Cleaning)
โ Parse messy columns (e.g., split โName_Age_Cityโ)
โ Regex to extract phone numbers, emails, URLs
โ Remove stopwords or HTML tags in text data
Example: Clean up a scraped dataset from LinkedIn bias
๐น 2. GroupBy and Aggregation with Pandas
โ Group sales data by product/region
โ Calculate avg, sum, count using .groupby()
โ Handle missing values smartly
Example: โWhatโs the top-selling product in each region?โ
๐น 3. SQL Join + Window Functions
โ INNER JOIN, LEFT JOIN to merge tables
โ ROW_NUMBER(), RANK(), LEAD(), LAG() for trends
โ Use CTEs to break complex queries
Example: โGet 2nd highest salary in each departmentโ
๐น 4. Data Structures: Lists, Dicts, Sets in Python
โ Use dictionaries to map, filter, and count
โ Remove duplicates with sets
โ List comprehensions for clean solutions
Example: โCount frequency of hashtags in tweetsโ
๐น 5. Basic Algorithms (Not DP or Graphs)
โ Sliding window for moving averages
โ Two pointers for duplicate detection
โ Binary search in sorted arrays
Example: โDetect if a pair of values sum to 100โ
๐ฏ Tip: Practice challenges that feel like real-world data work, not textbook CS exams.
Use platforms like:
StrataScratch
Hackerrank (SQL + Python)
Kaggle Code
I have curated the best interview resources to crack Data Science Interviews
๐๐
https://whatsapp.com/channel/0029Va8v3eo1NCrQfGMseL2D
Like if you need similar content ๐๐
โค1