[FE] Code Challenge - Tran Thanh Lam

src/problem1/README.md

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+# Problem 1: Three ways to sum to n
+
+## Description
+Provide 3 unique implementations of a function that calculates the summation of numbers from 1 to `n`.
+
+**Input**: `n` - any integer.
+**Output**: Summation to `n`.
+
+## Assumptions
+1. The result will always be less than `Number.MAX_SAFE_INTEGER`.
+2. Input `n` should be a non-negative integer.
+   - If `n` is 0, a sum is 0.
+   - If `n` < 0, the function throws an error (based on standard summation definition 1...n, though mathematical definition might return 0 or be invalid, here strict validation is applied).
+
+## Implementations
+
+### 1. `sum_to_n_a`: Arithmetic Series Formula
+Uses the mathematical formula for the sum of the first n integers:
+\[ S_n = \frac{n(n+1)}{2} \]
+
+- **Time Complexity**: O(1)—Constant time calculation.
+- **Space Complexity**: O(1)—Constant space.
+- **Pros**: Fastest and most efficient.
+- **Cons**: Theoretical risk of intermediate overflow `n*(n+1)` if `n` is extremely large (close to `MAX_SAFE_INTEGER`).
+
+### 2. `sum_to_n_b`: Iterative Loop
+Uses a `for` loop to accumulate the sum from 1 to `n`.
+
+- **Time Complexity**: O(n)—Linear time.
+- **Space Complexity**: O(1)—Constant space.
+- **Pros**: Robust, easy to read, no recursion stack limits.
+- **Cons**: Slower than the formula for very large `n`.
+
+### 3. `sum_to_n_c`: Recursion
+Uses the recursive definition: `sum(n) = n + sum(n-1)`.
+
+- **Time Complexity**: O(n)—Linear time.
+- **Space Complexity**: O(n)—Linear space due to the call stack.
+- **Pros**: Demonstrates functional programming concepts.
+- **Cons**: In JavaScript, this is limited by the maximum call stack size (typically ~10,000 calls). Will throw `RangeError: Maximum call stack size exceeded` for large `n`.
+
+## Usage
+```javascript
+import { sum_to_n_a } from './index'
+
+console.log(sum_to_n_a(5)); // 15
+```
+
+## Testing
+Run the test suite:
+```bash
+node src/problem1/test.js
+```

src/problem1/index.js

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+import { validateInput } from "./validation"
+
+// Option A: Arithmetic Series Formula | O(1) time, O(1) space
+export const sum_to_n_a = function(n) {
+  validateInput(n)
+
+  if (n === 0) return 0
+  return (n * (n + 1)) / 2
+}
+
+// Option B: Iterative Loop | O(n) time, O(1) space
+export const sum_to_n_b = function(n) {
+  validateInput(n)
+
+  let sum = 0
+  for (let i = 1; i <= n; i++) {
+    sum += i
+  }
+  return sum
+}
+
+// Option C: Recursion | O(n) time, O(n) space (stack)
+export const sum_to_n_c = function(n) {
+  if (n === 0) return 0
+  if (n === 1) return 1
+
+  validateInput(n)
+
+  if (n <= 1) return n
+  return n + sum_to_n_c(n - 1)
+}

src/problem1/test.js

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+import assert from "assert"
+import { sum_to_n_a, sum_to_n_b, sum_to_n_c } from "./index"
+
+const functions = [
+  { name: 'sum_to_n_a', fn: sum_to_n_a },
+  { name: 'sum_to_n_b', fn: sum_to_n_b },
+  { name: 'sum_to_n_c', fn: sum_to_n_c }
+]
+
+console.log("Starting Tests...\n")
+
+let passed = 0
+let failed = 0
+
+function runTest(testName, action) {
+  try {
+    action()
+    console.log(`✅ [PASS] ${testName}`)
+    passed++
+  } catch (e) {
+    console.error(`❌ [FAIL] ${testName}`)
+    console.error(`   Error: ${e.message}`)
+    failed++
+  }
+}
+
+functions.forEach(function(impl) {
+  const fn = impl.fn
+  const name = impl.name
+
+  console.log(`Testing implementation: ${name}`)
+
+  // Test Case 1: Standard Input
+  runTest(`${name}(5) should be 15`, function() {
+    assert.strictEqual(fn(5), 15)
+  })
+
+  // Test Case 2: Base Case 1
+  runTest(`${name}(1) should be 1`, function() {
+    assert.strictEqual(fn(1), 1)
+  })
+
+  // Test Case 3: Base Case 0
+  runTest(`${name}(0) should be 0`, function() {
+    assert.strictEqual(fn(0), 0)
+  })
+
+  // Test Case 4: Large Input (within stack limit for recursion)
+  runTest(`${name}(100) should be 5050`, function() {
+    assert.strictEqual(fn(100), 5050)
+  })
+
+  // Test Case 5: Negative Input
+  runTest(`${name}(-1) should throw Error`, function() {
+    assert.throws(function() {
+      return fn(-1)
+    }, /Input must be a non-negative integer/)
+  })
+
+  // Test Case 6: Non-integer Input
+  runTest(`${name}(5.5) should throw Error`, function() {
+    assert.throws(function() {
+      return fn(5.5)
+    }, /Input must be an integer/)
+  })
+
+  // Test Case 7: String Input
+  runTest(`${name}('5') should throw Error`, function() {
+    assert.throws(function() {
+      return fn('5')
+    }, /Input must be a number/)
+  })
+
+  console.log('---')
+})
+
+console.log(`\nTest Summary:`)
+console.log(`Total: ${passed + failed}`)
+console.log(`Passed: ${passed}`)
+console.log(`Failed: ${failed}`)
+
+if (failed > 0) {
+  process.exit(1)
+}

src/problem1/validation.js

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+/**
+ * Validates the input n for the sum_to_n function.
+ *
+ * @param {any} n - The input to validate.
+ * @throws {Error} If the input is invalid.
+ */
+export const validateInput = function(n) {
+  if (typeof n !== 'number') {
+    throw new Error("Input must be a number")
+  }
+
+  if (!Number.isInteger(n)) {
+    throw new Error("Input must be an integer")
+  }
+
+  if (n < 0) {
+    throw new Error("Input must be a non-negative integer")
+  }
+
+  if (n > Number.MAX_SAFE_INTEGER) {
+    throw new Error("Input exceeds MAX_SAFE_INTEGER")
+  }
+}

src/problem2/.gitignore

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+# Logs
+logs
+*.log
+npm-debug.log*
+yarn-debug.log*
+yarn-error.log*
+pnpm-debug.log*
+lerna-debug.log*
+
+node_modules
+dist
+dist-ssr
+*.local
+
+# Editor directories and files
+.vscode/*
+!.vscode/extensions.json
+.idea
+.DS_Store
+*.suo
+*.ntvs*
+*.njsproj
+*.sln
+*.sw?

src/problem2/.husky/pre-commit

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+lint-staged

src/problem2/README.md

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+# React + TypeScript + Vite
+
+This template provides a minimal setup to get React working in Vite with HMR and some ESLint rules.
+
+Currently, two official plugins are available:
+
+- [@vitejs/plugin-react](https://github.com/vitejs/vite-plugin-react/blob/main/packages/plugin-react) uses [Babel](https://babeljs.io/) (or [oxc](https://oxc.rs) when used in [rolldown-vite](https://vite.dev/guide/rolldown)) for Fast Refresh
+- [@vitejs/plugin-react-swc](https://github.com/vitejs/vite-plugin-react/blob/main/packages/plugin-react-swc) uses [SWC](https://swc.rs/) for Fast Refresh
+
+## React Compiler
+
+The React Compiler is currently not compatible with SWC. See [this issue](https://github.com/vitejs/vite-plugin-react/issues/428) for tracking the progress.
+
+## Expanding the ESLint configuration
+
+If you are developing a production application, we recommend updating the configuration to enable type-aware lint rules:
+
+```js
+export default defineConfig([
+  globalIgnores(['dist']),
+  {
+    files: ['**/*.{ts,tsx}'],
+    extends: [
+      // Other configs...
+
+      // Remove tseslint.configs.recommended and replace with this
+      tseslint.configs.recommendedTypeChecked,
+      // Alternatively, use this for stricter rules
+      tseslint.configs.strictTypeChecked,
+      // Optionally, add this for stylistic rules
+      tseslint.configs.stylisticTypeChecked,
+
+      // Other configs...
+    ],
+    languageOptions: {
+      parserOptions: {
+        project: ['./tsconfig.node.json', './tsconfig.app.json'],
+        tsconfigRootDir: import.meta.dirname,
+      },
+      // other options...
+    },
+  },
+])
+```
+
+You can also install [eslint-plugin-react-x](https://github.com/Rel1cx/eslint-react/tree/main/packages/plugins/eslint-plugin-react-x) and [eslint-plugin-react-dom](https://github.com/Rel1cx/eslint-react/tree/main/packages/plugins/eslint-plugin-react-dom) for React-specific lint rules:
+
+```js
+// eslint.config.js
+import reactX from 'eslint-plugin-react-x'
+import reactDom from 'eslint-plugin-react-dom'
+
+export default defineConfig([
+  globalIgnores(['dist']),
+  {
+    files: ['**/*.{ts,tsx}'],
+    extends: [
+      // Other configs...
+      // Enable lint rules for React
+      reactX.configs['recommended-typescript'],
+      // Enable lint rules for React DOM
+      reactDom.configs.recommended,
+    ],
+    languageOptions: {
+      parserOptions: {
+        project: ['./tsconfig.node.json', './tsconfig.app.json'],
+        tsconfigRootDir: import.meta.dirname,
+      },
+      // other options...
+    },
+  },
+])
+```

src/problem2/biome.json

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+{
+  "$schema": "https://biomejs.dev/schemas/2.3.11/schema.json",
+  "vcs": {
+    "enabled": true,
+    "clientKind": "git",
+    "useIgnoreFile": true
+  },
+  "files": {
+    "ignoreUnknown": false
+  },
+  "formatter": {
+    "enabled": true,
+    "indentStyle": "space",
+    "lineWidth": 100
+  },
+  "linter": {
+    "enabled": true,
+    "rules": {
+      "recommended": true,
+      "complexity": {
+        "noUselessFragments": "off"
+      },
+      "correctness": {
+        "useExhaustiveDependencies": "off"
+      },
+      "style": {
+        "useConsistentCurlyBraces": {
+          "level": "warn",
+          "fix": "safe"
+        }
+      }
+    }
+  },
+  "javascript": {
+    "formatter": {
+      "quoteStyle": "double",
+      "semicolons": "asNeeded",
+      "arrowParentheses": "asNeeded"
+    }
+  },
+  "assist": {
+    "enabled": true,
+    "actions": {
+      "source": {
+        "recommended": true
+      }
+    }
+  },
+  "css": {
+    "parser": {
+      "tailwindDirectives": true
+    }
+  }
+}

src/problem2/components.json

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+{
+  "$schema": "https://ui.shadcn.com/schema.json",
+  "style": "radix-mira",
+  "rsc": false,
+  "tsx": true,
+  "tailwind": {
+    "config": "",
+    "css": "src/index.css",
+    "baseColor": "neutral",
+    "cssVariables": true,
+    "prefix": ""
+  },
+  "iconLibrary": "lucide",
+  "menuColor": "default",
+  "menuAccent": "subtle",
+  "aliases": {
+    "components": "@/components",
+    "utils": "@/lib/utils",
+    "ui": "@/components/ui",
+    "lib": "@/lib",
+    "hooks": "@/hooks"
+  }
+}