Daily Coding Challenges & Projects

Frontend Mini Project Challenge

Theme : JavaScript Logical Puzzles & Debugging

Small Challenge : JavaScript Logical Puzzle

Write a function mystery(arr) that returns the second most frequent element in an array without using any sorting.

Example :

mystery([1, 2, 2, 3, 3, 3]) → 2

JavaScript Debugging Challenge :

Buggy Code :

function add(a, b) {
  return a + b;
}
console.log(add("5", 3));

Question :

Why is the output "53" instead of 8?

Fix the issue without modifying the function name or parameters

Backend Challenge

Focus : C, C++, C#

C Challenge : Pointer Logic

Write a C function to rotate an array right by k steps in-place without using an extra array.

C++ Challenge : Class & Memory

Create a C++ class Matrix that:

• Dynamically allocates a 2D matrix
• Implements a deep copy constructor
• Supports add() to add two matrices

C# Challenge : LINQ + Async

Write an async C# method that:

• Reads a text file line-by-line
• Uses LINQ to filter lines containing more than 3 words
• Returns them as a list

Database Query Challenge

Problems on SQL - HR Database :

1. Find employees who joined in the last 90 days.
2. Find employees who never received a salary increase (compare salary history table with employee table).

Data Structures & Algorithms Challenge

• Easy : Frequency Check
• Problem : Given an array, return true if all frequencies are unique, else false.
• Hint :Use a frequency map → convert values into a set → compare sizes.
• Medium : Find Peak Element
• Problem : Find any peak element (greater than neighbors) in O(log n).
• Hint :Binary search: compare mid with mid+1.
• Hard : Reconstruct Itinerary
• Problem : Given airline tickets [(from → to)], reconstruct the lexicographically smallest itinerary starting at "JFK".
• Hint :Hierholzer’s Algorithm + min-heap adjacency list.

Bug of the Day

Focus : C, C++, C#

Buggy Code ( C ) :

int arr[5];
for (int i = 0; i <= 5; i++) {
    arr[i] = i * 2;
}

Challenge : Find & fix the issue.

Buggy Code ( C++ ) :

string s = "Hello";
cout << s[5];

Challenge : What’s wrong? How do you fix it?

Buggy Code ( C# ) :

int x = null;
Console.WriteLine(x);

Challenge : Identify the error and correct it.

📋 Daily Micro-Project

Focus : Frontend

Task :

Build a “Pulsing Notification Badge” using CSS + JS

• A red circular badge
• Pulsing animation
• Click → count resets to zero
• No external libraries

Trivia: 5 Fun Facts

1. JavaScript was created in 10 days by Brendan Eich.
2. C was originally invented to rewrite the UNIX kernel.
3. C# was first named Cool (“C-like Object-Oriented Language”).
4. The first computer bug was literally a moth stuck inside a relay.
5. The name “Python” comes from Monty Python, not the snake.

Tool & Resource of the Day

Tool : ESLint

A static code analysis tool for JavaScript/TypeScript that catches bugs before runtime

Resource Roundup ( JavaScript Debugging ) :

• "JS Debugging Handbook" — Free PDF
• Chrome DevTools Console Cheat Sheet
• Online playground: CodeSandbox Debug Mode

Interview Question of the Day

Daily Interview Questions

Frontend :
1. Why is == dangerous in JavaScript?
2. What is event bubbling?
3. Explain how closures work with an example.
4. What is a pure function and why is it important?

Backend :
1. Difference between a process and a thread?
2. What is a deadlock?
3. Explain how garbage collection works in C#.
4. Explain REST statelessness

Database :
1. What is a composite primary key?
2. Explain clustered vs non-clustered index.
3. What is ACID?

Others :
1. What is a kernel in OS?
2. What is virtualization?

Daily Quiz Challenge

Frontend :

1. What is the output?

console.log([] + {});

2. Which CSS unit is relative to the viewport width?
3. What does event.preventDefault() do?

Backend :

1. What is the output of:

printf("%d", 5/2);

2. Which C++ keyword prevents inheritance?
3. What is C# async used for?

Database :

1. Which SQL clause is applied after GROUP BY?

Other :

1. Which protocol does SSH use?

Mixed Quiz :

1. JavaScript: What does typeof NaN return?
2. SQL: What does COUNT(*) count?
3. C: What does malloc() return on failure?

Weekly Cross-Domain Activities ( November 28 to December 04, 2025 )

API of the Day:

Use the Currency Exchange API to convert an amount between currencies.

Linux / DevOps Tip :

Run server health check :

top  
htop  
df -h  
du -sh *  
free -m  
uptime  
journalctl -xe  
systemctl status <service>

Real-World Project of the Week ( November 28 to December 04, 2025 )

Project of the Week:

Build a URL shortener app ( frontend + backend + database ).

Collaborative Project :

Join an open-source project:

“Awesome-DSA-Practice”

(Create algorithms + solutions in multiple languages.)

Case Study :

Analyze how Spotify recommendation engine works.

Users replicate the feature using:

• Cosine similarity
• TF-IDF
• Collaborative filtering