[BE] Code challenge - Trong Quan

src/problem4/index.ts

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+/**
+ * Problem 4: Three ways to sum to n
+ *
+ * Contract used for any integer n:
+ * - n > 0:  1 + 2 + ... + n
+ * - n < 0: -1 + -2 + ... + n
+ * - n = 0:  0
+ */
+
+export function sum_to_n_a(n: number): number {
+  // Arithmetic formula.
+  // Time: O(1), Space: O(1). This is the most efficient implementation.
+  const sign = n < 0 ? -1 : 1;
+  const absoluteN = Math.abs(n);
+
+  return sign * ((absoluteN * (absoluteN + 1)) / 2);
+}
+
+export function sum_to_n_b(n: number): number {
+  // Iterative accumulation.
+  // Time: O(|n|), Space: O(1). Simple and memory-efficient, but slower for large |n|.
+  let total = 0;
+  const step = n < 0 ? -1 : 1;
+
+  for (let current = step; n < 0 ? current >= n : current <= n; current += step) {
+    total += current;
+  }
+
+  return total;
+}
+
+export function sum_to_n_c(n: number): number {
+  // Functional implementation using array generation and reduce.
+  // Time: O(|n|), Space: O(|n|). Clear as a demonstration, but less efficient
+  // because it allocates an array with one element per number being summed.
+  const sign = n < 0 ? -1 : 1;
+  const absoluteN = Math.abs(n);
+
+  return Array.from({ length: absoluteN }, (_, index) => sign * (index + 1)).reduce(
+    (total, value) => total + value,
+    0,
+  );
+}
+

src/problem5/README.md

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+# Problem 5: A Crude Server
+
+This is a small ExpressJS + TypeScript CRUD server for managing books.
+
+The service persists data to a JSON database file at `data/database.json` by default. You can override that path with `DATABASE_FILE`.
+
+## Requirements
+
+- Node.js 20+
+- npm
+
+## Install
+
+From the repository root:
+
+```bash
+cd backend_test/problem5
+npm install
+```
+
+## Run In Development
+
+```bash
+npm run dev
+```
+
+The server starts on `http://localhost:3000`.
+
+To use another port:
+
+```bash
+PORT=4000 npm run dev
+```
+
+To use another database file:
+
+```bash
+DATABASE_FILE=./data/local.json npm run dev
+```
+
+## Build And Run
+
+```bash
+npm run build
+npm start
+```
+
+## API
+
+### Health Check
+
+```bash
+curl http://localhost:3000/health
+```
+
+### Create A Book
+
+```bash
+curl -X POST http://localhost:3000/books \
+  -H "Content-Type: application/json" \
+  -d '{
+    "title": "Clean Code",
+    "author": "Robert C. Martin",
+    "status": "available",
+    "publishedYear": 2008
+  }'
+```
+
+Fields:
+
+- `title`: required string
+- `author`: required string
+- `status`: optional, one of `available`, `borrowed`, `archived`
+- `publishedYear`: optional integer
+
+### List Books
+
+```bash
+curl http://localhost:3000/books
+```
+
+Basic filters:
+
+```bash
+curl "http://localhost:3000/books?status=available"
+curl "http://localhost:3000/books?author=martin"
+curl "http://localhost:3000/books?q=clean"
+```
+
+### Get Book Details
+
+```bash
+curl http://localhost:3000/books/:id
+```
+
+### Update A Book
+
+```bash
+curl -X PATCH http://localhost:3000/books/:id \
+  -H "Content-Type: application/json" \
+  -d '{
+    "status": "borrowed"
+  }'
+```
+
+### Delete A Book
+
+```bash
+curl -X DELETE http://localhost:3000/books/:id
+```
+
+Successful deletes return `204 No Content`.
+

src/problem5/dist/app.js

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+"use strict";
+var __importDefault = (this && this.__importDefault) || function (mod) {
+    return (mod && mod.__esModule) ? mod : { "default": mod };
+};
+Object.defineProperty(exports, "__esModule", { value: true });
+exports.app = void 0;
+const cors_1 = __importDefault(require("cors"));
+const express_1 = __importDefault(require("express"));
+const helmet_1 = __importDefault(require("helmet"));
+const morgan_1 = __importDefault(require("morgan"));
+const zod_1 = require("zod");
+const bookRepository_1 = require("./bookRepository");
+const validation_1 = require("./validation");
+exports.app = (0, express_1.default)();
+exports.app.use((0, helmet_1.default)());
+exports.app.use((0, cors_1.default)());
+exports.app.use(express_1.default.json());
+exports.app.use((0, morgan_1.default)("dev"));
+exports.app.get("/health", (_req, res) => {
+    res.json({ status: "ok" });
+});
+exports.app.post("/books", async (req, res, next) => {
+    try {
+        const input = validation_1.createBookSchema.parse(req.body);
+        const book = await (0, bookRepository_1.createBook)(input);
+        res.status(201).json({ data: book });
+    }
+    catch (error) {
+        next(error);
+    }
+});
+exports.app.get("/books", async (req, res, next) => {
+    try {
+        const filters = validation_1.listBookQuerySchema.parse(req.query);
+        const books = await (0, bookRepository_1.listBooks)(filters);
+        res.json({ data: books, count: books.length });
+    }
+    catch (error) {
+        next(error);
+    }
+});
+exports.app.get("/books/:id", async (req, res, next) => {
+    try {
+        const book = await (0, bookRepository_1.getBookById)(req.params.id);
+        if (!book) {
+            res.status(404).json({ error: "Book not found" });
+            return;
+        }
+        res.json({ data: book });
+    }
+    catch (error) {
+        next(error);
+    }
+});
+exports.app.patch("/books/:id", async (req, res, next) => {
+    try {
+        const input = validation_1.updateBookSchema.parse(req.body);
+        const book = await (0, bookRepository_1.updateBook)(req.params.id, input);
+        if (!book) {
+            res.status(404).json({ error: "Book not found" });
+            return;
+        }
+        res.json({ data: book });
+    }
+    catch (error) {
+        next(error);
+    }
+});
+exports.app.delete("/books/:id", async (req, res, next) => {
+    try {
+        const deleted = await (0, bookRepository_1.deleteBook)(req.params.id);
+        if (!deleted) {
+            res.status(404).json({ error: "Book not found" });
+            return;
+        }
+        res.status(204).send();
+    }
+    catch (error) {
+        next(error);
+    }
+});
+exports.app.use((_req, res) => {
+    res.status(404).json({ error: "Route not found" });
+});
+exports.app.use((error, _req, res, _next) => {
+    if (error instanceof zod_1.ZodError) {
+        res.status(400).json({
+            error: "Validation failed",
+            details: error.flatten(),
+        });
+        return;
+    }
+    console.error(error);
+    res.status(500).json({ error: "Internal server error" });
+});

src/problem5/dist/bookRepository.js

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+"use strict";
+Object.defineProperty(exports, "__esModule", { value: true });
+exports.listBooks = listBooks;
+exports.getBookById = getBookById;
+exports.createBook = createBook;
+exports.updateBook = updateBook;
+exports.deleteBook = deleteBook;
+const crypto_1 = require("crypto");
+const database_1 = require("./database");
+async function listBooks(filters) {
+    const data = await database_1.database.read();
+    const author = filters.author?.toLowerCase();
+    const query = filters.q?.toLowerCase();
+    return data.books.filter((book) => {
+        if (filters.status && book.status !== filters.status) {
+            return false;
+        }
+        if (author && !book.author.toLowerCase().includes(author)) {
+            return false;
+        }
+        if (query) {
+            const searchable = `${book.title} ${book.author}`.toLowerCase();
+            if (!searchable.includes(query)) {
+                return false;
+            }
+        }
+        return true;
+    });
+}
+async function getBookById(id) {
+    const data = await database_1.database.read();
+    return data.books.find((book) => book.id === id) ?? null;
+}
+async function createBook(input) {
+    const data = await database_1.database.read();
+    const now = new Date().toISOString();
+    const book = {
+        id: (0, crypto_1.randomUUID)(),
+        ...input,
+        createdAt: now,
+        updatedAt: now,
+    };
+    data.books.push(book);
+    await database_1.database.write(data);
+    return book;
+}
+async function updateBook(id, input) {
+    const data = await database_1.database.read();
+    const index = data.books.findIndex((book) => book.id === id);
+    if (index === -1) {
+        return null;
+    }
+    const updatedBook = {
+        ...data.books[index],
+        ...input,
+        updatedAt: new Date().toISOString(),
+    };
+    data.books[index] = updatedBook;
+    await database_1.database.write(data);
+    return updatedBook;
+}
+async function deleteBook(id) {
+    const data = await database_1.database.read();
+    const nextBooks = data.books.filter((book) => book.id !== id);
+    if (nextBooks.length === data.books.length) {
+        return false;
+    }
+    data.books = nextBooks;
+    await database_1.database.write(data);
+    return true;
+}

src/problem5/dist/database.js

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+"use strict";
+var __importDefault = (this && this.__importDefault) || function (mod) {
+    return (mod && mod.__esModule) ? mod : { "default": mod };
+};
+Object.defineProperty(exports, "__esModule", { value: true });
+exports.database = exports.JsonDatabase = void 0;
+const fs_1 = require("fs");
+const path_1 = __importDefault(require("path"));
+const defaultDatabase = {
+    books: [],
+};
+class JsonDatabase {
+    constructor(filePath) {
+        this.filePath = filePath;
+    }
+    async read() {
+        await this.ensureFile();
+        const content = await fs_1.promises.readFile(this.filePath, "utf8");
+        return JSON.parse(content);
+    }
+    async write(data) {
+        await fs_1.promises.mkdir(path_1.default.dirname(this.filePath), { recursive: true });
+        await fs_1.promises.writeFile(this.filePath, `${JSON.stringify(data, null, 2)}\n`, "utf8");
+    }
+    async ensureFile() {
+        try {
+            await fs_1.promises.access(this.filePath);
+        }
+        catch {
+            await this.write(defaultDatabase);
+        }
+    }
+}
+exports.JsonDatabase = JsonDatabase;
+const databasePath = process.env.DATABASE_FILE
+    ? path_1.default.resolve(process.env.DATABASE_FILE)
+    : path_1.default.resolve(__dirname, "../data/database.json");
+exports.database = new JsonDatabase(databasePath);

src/problem5/dist/server.js

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+"use strict";
+Object.defineProperty(exports, "__esModule", { value: true });
+const app_1 = require("./app");
+const port = Number(process.env.PORT ?? 3000);
+app_1.app.listen(port, () => {
+    console.log(`Problem 5 server is running on http://localhost:${port}`);
+});

src/problem5/dist/types.js

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+"use strict";
+Object.defineProperty(exports, "__esModule", { value: true });

src/problem5/dist/validation.js

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+"use strict";
+Object.defineProperty(exports, "__esModule", { value: true });
+exports.listBookQuerySchema = exports.updateBookSchema = exports.createBookSchema = exports.bookStatusSchema = void 0;
+const zod_1 = require("zod");
+exports.bookStatusSchema = zod_1.z.enum(["available", "borrowed", "archived"]);
+exports.createBookSchema = zod_1.z.object({
+    title: zod_1.z.string().trim().min(1, "title is required"),
+    author: zod_1.z.string().trim().min(1, "author is required"),
+    status: exports.bookStatusSchema.default("available"),
+    publishedYear: zod_1.z.number().int().min(0).max(9999).optional(),
+});
+exports.updateBookSchema = exports.createBookSchema.partial().refine((value) => Object.keys(value).length > 0, "at least one field is required");
+exports.listBookQuerySchema = zod_1.z.object({
+    status: exports.bookStatusSchema.optional(),
+    author: zod_1.z.string().trim().optional(),
+    q: zod_1.z.string().trim().optional(),
+});