🔍 Mini Search Engine- Document Indexing System

Java | Data Structures | React | REST API

A keyword-based search engine built from scratch using Java and core data structures, implementing an inverted index for fast document retrieval and a React + Vite frontend for real-time search interaction.

This project demonstrates algorithmic thinking, backend system design, and full-stack integration, making it suitable for SDE / Backend / Full-Stack internship roles.

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✨ Highlights (Quick Scan)

• ⚡ Inverted Index using HashMap<String, Set<Integer>>
• 🚀 O(1) average-time keyword search
• 🌐 RESTful API built in Java
• 🎨 Premium React UI with cards & keyword highlighting
• 🔗 End-to-end backend ↔ frontend integration
• 📊 Time–space complexity analysis

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🧠 How It Works (High Level)

User Search (React UI) ↓ REST API Call (/search?q=keyword) ↓ Java Backend (Search Service) ↓ Inverted Index Lookup (HashMap) ↓ Matching Documents Returned as JSON

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⚙️ Tech Stack

Backend

• Java 17
• Data Structures: HashMap, HashSet
• Inverted Index
• REST API (Spark Java)
• Maven
• Gson

Frontend

• React
• Vite
• JavaScript (ES6+)
• HTML5
• CSS3 (custom styling)

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🧩 Core Feature — Inverted Index

Instead of scanning every document on each search, documents are preprocessed into an inverted index:

java    → [1, 3]
search  → [2]
engine  → [2]

This enables fast keyword-based retrieval and demonstrates real-world search engine fundamentals.

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⏱️ Algorithm & Complexity Analysis

Index Construction

Time Complexity: O(N × W)

N → number of documents

W → average words per document

Search Operation

Time Complexity: O(1) (average case)

Space Complexity

O(K + D)

🎨 UI Preview (What the User Sees)

Clean search input

Card-based result layout

Document preview text

Highlighted matching keywords

Minimal, professional UI

(Frontend communicates with backend via REST API)

K → unique keywords

D → document references

Demonstrates effective time–space tradeoff optimization using hash-based indexing.

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📂 Project Structure

Search-engine/
├── backend/
│   ├── src/main/java/
│   │   ├── api/
│   │   ├── index/
│   │   ├── model/
│   │   ├── service/
│   │   └── app/
│   └── pom.xml
│
├── frontend/
│   ├── src/
│   │   ├── components/
│   │   ├── App.jsx
│   │   └── index.css
│
└── README.md

🚀 Run Locally

Backend (Java) cd backend mvn clean compile mvn exec:java

Server runs at:

http://localhost:4567

Test API:

http://localhost:4567/search?q=java

Frontend (React)

cd frontend
npm install
npm run dev

Frontend runs at:

http://localhost:5173

⭐ Why This Project Matters

This project goes beyond tutorials and demonstrates real backend logic, algorithmic efficiency, and full-stack execution, making it a strong addition to an SDE internship or entry-level software engineering resume.