[BE] Coding Challenge - Arthur Okolo

.gitignore

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+# Dependencies
+node_modules/
+npm-debug.log*
+yarn-debug.log*
+yarn-error.log*
+package-lock.json
+yarn.lock
+
+# Environment variables
+.env
+.env.local
+.env.*.local
+
+# IDE
+.vscode/
+.idea/
+*.swp
+*.swo
+*~
+
+# OS
+.DS_Store
+Thumbs.db
+
+# Build outputs
+dist/
+build/
+*.log
+
+# Database
+*.sqlite
+*.sqlite3
+*.db
+
+# Temporary files
+*.tmp
+.cache/

src/problem4/sum_n.ts

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+// ===============================
+// Implementation A — Iterative
+// ===============================
+
+// Complexity
+// Time: O(n) — iterates from 1 to n
+// Space: O(1) — constant extra memory
+//
+// Notes:
+// - Very readable and safe
+// - Slightly slower for large n due to iteration
+// - Best when clarity is preferred over performance
+export const sum_to_n_a = (n: number): number => {
+	let sum = 0;
+	for (let i = 1; i <= n; i++) {
+		sum += i;
+	}
+	return sum;
+};
+
+// ===============================
+// Implementation B — Mathematical Formula
+// ===============================
+
+// Complexity
+// Time: O(1) — constant time calculation
+// Space: O(1) — constant extra memory
+//
+// Notes:
+// - Most efficient implementation
+// - No loops or recursion
+// - Safe under the assumption that the result
+//   is less than Number.MAX_SAFE_INTEGER
+export const sum_to_n_b = (n: number): number => {
+	return (n * (n + 1)) / 2;
+};
+
+// ===============================
+// Implementation C — Recursive
+// ===============================
+
+// Complexity
+// Time: O(n) — one recursive call per decrement
+// Space: O(n) — call stack grows linearly
+//
+// Notes:
+// - Elegant and expressive
+// - Inefficient for large n due to recursion overhead
+// - Risk of stack overflow; not recommended for production
+export const sum_to_n_c = (n: number): number => {
+	if (n <= 1) return n;
+	return n + sum_to_n_c(n - 1);
+};

src/problem5/README.md

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+# Resource Management API
+
+A RESTful backend server built with Express.js and TypeScript that provides CRUD operations for managing resources. The application uses TypeORM with SQLite for data persistence.
+
+## Features
+
+- ✅ Create a resource
+- ✅ List resources with pagination and filtering
+- ✅ Get details of a specific resource
+- ✅ Update resource details
+- ✅ Delete a resource
+
+## Tech Stack
+
+- **Runtime**: Node.js
+- **Framework**: Express.js
+- **Language**: TypeScript
+- **ORM**: TypeORM
+- **Database**: SQLite
+- **Validation**: Zod
+
+## Prerequisites
+
+- Node.js (v14 or higher)
+- npm or yarn
+
+## Installation
+
+1. Install dependencies:
+```bash
+npm install
+```
+
+## Configuration
+
+The application uses SQLite database which is automatically created as `database.sqlite` in the project root. No additional configuration is required for development.
+
+The server runs on port `3000` by default. You can change this by setting the `PORT` environment variable:
+
+```bash
+export PORT=3000  # Linux/Mac
+set PORT=3000     # Windows
+```
+
+## Running the Application
+
+### Development Mode
+
+Run the server in development mode with hot-reload:
+
+```bash
+npm run dev
+```
+
+The server will start on `http://localhost:3000` (or the port specified in the `PORT` environment variable).
+
+### Production Mode
+
+1. Build the TypeScript code:
+```bash
+npm run build
+```
+
+2. Start the server:
+```bash
+npm start
+```
+
+## API Endpoints
+
+All endpoints are prefixed with `/resources`.
+
+### Create a Resource
+
+```http
+POST /resources
+Content-Type: application/json
+
+{
+  "name": "My Resource",
+  "description": "Resource description (optional)"
+}
+```
+
+**Response**: `201 Created` with the created resource
+
+### List Resources
+
+```http
+GET /resources?page=1&limit=10&name=search
+```
+
+**Query Parameters**:
+- `page` (optional): Page number (default: 1)
+- `limit` (optional): Items per page (default: 10)
+- `name` (optional): Filter by name
+
+**Response**: `200 OK` with paginated list of resources
+
+### Get Resource Details
+
+```http
+GET /resources/:id
+```
+
+**Response**: `200 OK` with resource details or `404 Not Found`
+
+### Update a Resource
+
+```http
+PUT /resources/:id
+Content-Type: application/json
+
+{
+  "name": "Updated Name",
+  "description": "Updated description"
+}
+```
+
+**Response**: `200 OK` with updated resource or `404 Not Found`
+
+### Delete a Resource
+
+```http
+DELETE /resources/:id
+```
+
+**Response**: `204 No Content` on success or `400 Bad Request` if ID is invalid
+
+## Project Structure
+
+```
+src/
+├── app.ts                 # Express app configuration
+├── server.ts              # Server entry point
+├── database.ts            # TypeORM data source configuration
+└── resource/
+    ├── resource.controller.ts    # Request handlers
+    ├── resource.usecases.ts      # Business logic
+    ├── resource.repository.ts    # Data access layer
+    ├── resource.orm-entity.ts    # TypeORM entity
+    └── resource.routes.ts        # Route definitions
+```
+
+## License
+
+ISC

src/problem5/package.json

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+{
+  "name": "problem5",
+  "version": "1.0.0",
+  "main": "server.js",
+  "scripts": {
+    "dev": "ts-node-dev --respawn --transpile-only src/server.ts",
+    "build": "tsc",
+    "start": "node dist/server.js",
+    "test": "echo \"Error: no test specified\" && exit 1"
+  },
+  "keywords": [],
+  "author": "",
+  "license": "ISC",
+  "description": "",
+  "dependencies": {
+    "dotenv": "^17.2.3",
+    "express": "^5.2.1",
+    "reflect-metadata": "^0.2.2",
+    "sqlite3": "^5.1.7",
+    "typeorm": "^0.3.28",
+    "zod": "^4.3.5"
+  },
+  "devDependencies": {
+    "@types/express": "^5.0.6",
+    "@types/node": "^25.0.9",
+    "ts-node-dev": "^2.0.0",
+    "typescript": "^5.9.3"
+  }
+}

src/problem5/src/api-test.http

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+### Create a Resource
+POST http://localhost:3000/resources
+Content-Type: application/json
+
+{
+  "name": "My Test Resource",
+  "description": "Hello REST Client"
+}
+
+### List Resources
+GET http://localhost:3000/resources?page=1&limit=5
+
+### Get a single Resource
+GET http://localhost:3000/resources/890ae7b9-9c96-406f-b64b-2b24efeeedeb
+
+### Update a Resource
+PUT http://localhost:3000/resources/890ae7b9-9c96-406f-b64b-2b24efeeedeb
+Content-Type: application/json
+
+{
+  "name": "Updated Resource",
+  "description": "Updated description"
+}
+
+### Delete a Resource
+DELETE http://localhost:3000/resources/1

src/problem5/src/app.ts

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+import express from "express";
+import resourceRoutes from "./resource/resource.routes";
+import { AppDataSource } from "./database";
+
+export const createApp = async () => {
+  await AppDataSource.initialize();
+  const app = express();
+  app.use(express.json());
+  app.use("/resources", resourceRoutes);
+  return app;
+};

src/problem5/src/database.ts

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+import "reflect-metadata";
+import { DataSource } from "typeorm";
+import { ResourceOrmEntity } from "./resource/resource.orm-entity";
+
+export const AppDataSource = new DataSource({
+  type: "sqlite",
+  database: "database.sqlite",
+  synchronize: true,
+  entities: [ResourceOrmEntity],
+});