Clever Engineer

𝗜𝗻𝘁𝗲𝗿𝗳𝗮𝗰𝗲𝘀 𝗘𝘅𝗽𝗹𝗮𝗶𝗻

In object-oriented design, interfaces help us build flexible, testable, and loosely connected systems. They act like contracts: they define what must be done, but not how it should be done.

1. What is an Interface?

An interface lists method names that any class must provide.

It doesn’t care about the internal logic, only the structure.

Analogy:

Think of a remote control:

play()

pause()

volumeUp()

powerOff()

No matter if it controls a TV, a speaker, or a projector — the buttons stay the same, but the actions behind them differ.

That’s exactly how interfaces work in code.

2. Why Use Interfaces?

Define behavior, not details → They say what should happen, but not how.

Enable polymorphism → Different classes can follow the same interface in their own way.

Promote decoupling → Code depends on the interface, not the concrete class, so changes in implementation don’t break everything else.

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𝐖𝐡𝐚𝐭 𝐢𝐬 𝐋𝐨𝐰-𝐋𝐞𝐯𝐞𝐥 𝐃𝐞𝐬𝐢𝐠𝐧 (𝐋𝐋𝐃)?

In software engineering, Low-Level Design (LLD) is where abstract concepts are turned into practical, working blueprints. It’s the step where a High-Level Design (HLD) is broken down into detailed class diagrams, interfaces, object relationships, and design patterns.

What LLD Really Means

LLD answers the question: “How exactly will we implement this?

HLD says: “We need a Ride-Sharing Service.”

LLD says: “We’ll create an interface RideAllocator with implementations like NearestDriverAllocator and CheapestDriverAllocator, both coordinated by a RideManager.”

LLD zooms in on the building blocks of your system. It ensures the software is modular, extendable, testable, and understandable. It’s not just about making something work—it’s about designing systems that can adapt and grow.

Core Components of LLD

1. Classes and Objects

This is where design begins: defining the key entities.

Ask yourself:

What classes represent the main concepts?

What responsibilities do they have?

What data do they hold?

What actions do they perform?

Example: In a library management system, we might define:

Book – stores title, author, and availability

Member – borrows and returns books

Librarian – manages inventory

Loan – represents the borrowing transaction

2. Interfaces and Abstractions

Interfaces define contracts between components. They ensure loose coupling so implementations can change without breaking the system.

Ask yourself:

What should a class expose to the outside?

Which details should remain hidden?

What can be abstracted behind an interface?

Example: A SearchEngine interface could have multiple implementations:

ElasticSearchEngine

SolrSearchEngine

InMemorySearchEngine

The system depends only on the SearchEngine interface, not on the concrete choice.

3. Relationships Between Classes

Classes interact with each other in structured ways. LLD defines these relationships clearly:

Association – a general “uses-a” relationship

Composition – strong “has-a” (lifespan tied)

Aggregation – weaker “has-a” (independent lifespan)

Inheritance – “is-a” relationship for shared behavior

Example:

A Library has many Books (composition).

A Member can borrow multiple Books (one-to-many).

A Librarian manages several Members (aggregation).

4. Method Signatures

Once the structure is clear, you define operations.

Ask:

What methods should each class have?

What parameters and return types are needed?

Should they be synchronous or asynchronous?

What exceptions could they throw?

Bad: void doTask(String s)Better: void borrowBook(Book book, Member member)

The improved method is clearer, domain-specific, and more extensible.

Read More here

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𝐓𝐡𝐢𝐬 𝐢𝐬 𝐚 𝐛𝐞𝐚𝐮𝐭𝐢𝐟𝐮𝐥 𝐐𝐮𝐞𝐬𝐭𝐢𝐨𝐧

Given an array nums containing n distinct numbers in the range [0, n], return the only number in the range that is missing from the array.

𝐄𝐱𝐚𝐦𝐩𝐥𝐞 𝟏:

Input: nums = [3,0,1]

Output: 2

𝐄𝐱𝐩𝐥𝐚𝐧𝐚𝐭𝐢𝐨𝐧:

n = 3 since there are 3 numbers, so all numbers are in the range [0,3]. 2 is the missing number in the range since it does not appear in nums.

𝐈𝐧𝐭𝐮𝐢𝐭𝐢𝐨𝐧

There are actually two ways to solve this problem either you use logic cancellation or the sum of real numbers.

𝐀𝐩𝐩𝐫𝐨𝐚𝐜𝐡

The Approach for the sum of real number is given as follow we know that for any real number you can find the sum by saying n(n+1)/2 this is a formular in arthmentic progression if you want the sum form 1 to 5 5(5+1)/2 = 15 it equal to 1+2+3+4+5 = 15

we can compute the summation of the array and substract the actual sum form the expected sum the result is the missing number.

Complexity

Time complexity:

O(n)

Space complexity:

O(1)

𝐀𝐩𝐩𝐫𝐨𝐚𝐜𝐡 𝐍𝐮𝐦𝐛𝐞𝐫 𝟐

The second is using the theory of logic

the following are true for xor

a ^ a = 0
a ^ 0 = a

equip with this knowledge we can Try to generate two group and cancel out where needed

Group 1 , 0, 1, 2, 3 or (0 ^ 1 ^ 2 ^ 3)

Group 2, 3, 0, 1 or (3 ^ 0 ^ 1)

we can combine them

(0 ^ 1 ^ 2 ^ 3) ^ (3 ^ 0 ^ 1)

let combine like term

0 ^ 0 ^ 1 ^ 1 ^ 3 ^ 3 ^ 2 = 2

The following two solution have the same time and space complexity

The actual solution is here

https://shorturl.at/XJU06

Remember it good to be smart but what even better is being consistent. Stay humble stay loyal to your grind

𝗥𝗘𝗦𝗧 𝗔𝗣𝗜𝘀: 𝗧𝗵𝗲 𝗖𝗼𝗻𝗲𝗿𝘀𝘁𝗼𝗻𝗲 𝗼𝗳 𝗠𝗼𝗱𝗲𝗿𝗻 𝗪𝗲𝗯 𝗗𝗲𝘃𝗲𝗹𝗼𝗽𝗺𝗲𝗻𝘁

As a software engineer, I've always been passionate about sharing my knowledge and simplifying complex technical concepts. This presentation on REST APIs aims to provide a comprehensive understanding

Let's dive into the world of REST APIs with an analogy that might resonate.

Think of a REST API as a waiter at a restaurant. You, the client (or in API terms, the user), sit at the table (your device) and request a menu (data). The waiter (REST API) takes your order (request) to the kitchen (server), and soon enough, your dish (response) arrives.

Now, just like a restaurant has various actions – ordering, updating preferences, or even canceling an order – a REST API has different methods:

𝗚𝗘𝗧: Fetches specific data.
𝗣𝗢𝗦𝗧: Adds new data.
𝗣𝗨𝗧: Updates existing data.
𝐃𝐄𝐋𝐄𝐓𝐄: Removes specific data.
𝗣𝗔𝗧𝗖𝗛: Makes partial updates.

Responses from the API are like the waiter's service – either successful (your order is delivered) or an error (oops, kitchen couldn't handle it).

Understanding this helps whether you're into software or just curious about how things online work together. I made this simple presentation to break down the basics of REST APIs. If you're diving into tech or just want to know more, I'm here to help. Expect more easy-to-understand stuff from me in the future! Got questions or thoughts? Let's chats

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