[FE] Code Challenge - Loc Nguyen

src/problem1/index.ts

@@ -0,0 +1,42 @@
+// Mathematic | Time O(1) - Space O(1)
+export function sum_to_n_a(n: number): number {
+  return (n * (n + 1)) / 2;
+}
+
+// Iterative | Time O(n) - Space O(1)
+export function sum_to_n_b(n: number): number {
+  let total = 0;
+  for (let i = 1; i <= n; i++) {
+    total += i;
+  }
+  return total;
+}
+
+// Recursive | Time O(n) - Space O(n)
+export function sum_to_n_c(n: number): number {
+  if (n <= 0) return 0;
+  return n + sum_to_n_c(n - 1);
+}
+
+// Performance test
+const testCases = [1_00, 1_000, 10_000];
+
+for (const n of testCases) {
+  console.log(`\n--- n = ${n.toLocaleString()} ---`);
+
+  let t = performance.now();
+  console.log(
+    `sum_to_n_a (Math): ${sum_to_n_a(n)} | ${(performance.now() - t).toFixed(4)}ms`,
+  );
+
+  t = performance.now();
+  console.log(
+    `sum_to_n_b (Iterative): ${sum_to_n_b(n)} | ${(performance.now() - t).toFixed(4)}ms`,
+  );
+
+  // Recursive blows the stack for large n, cap it
+  t = performance.now();
+  console.log(
+    `sum_to_n_c (Recursive): ${sum_to_n_c(n)} | ${(performance.now() - t).toFixed(4)}ms`,
+  );
+}

src/problem2/fancy-form/.gitignore

@@ -0,0 +1,24 @@
+# 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/fancy-form/README.md

@@ -0,0 +1,75 @@
+# 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 enabled on this template. See [this documentation](https://react.dev/learn/react-compiler) for more information.
+
+Note: This will impact Vite dev & build performances.
+
+## 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/fancy-form/components.json

@@ -0,0 +1,23 @@
+{
+  "$schema": "https://ui.shadcn.com/schema.json",
+  "style": "new-york",
+  "rsc": false,
+  "tsx": true,
+  "tailwind": {
+    "config": "",
+    "css": "src/index.css",
+    "baseColor": "neutral",
+    "cssVariables": true,
+    "prefix": ""
+  },
+  "iconLibrary": "lucide",
+  "rtl": false,
+  "aliases": {
+    "components": "@/components",
+    "utils": "@/lib/utils",
+    "ui": "@/components/ui",
+    "lib": "@/lib",
+    "hooks": "@/hooks"
+  },
+  "registries": {}
+}

src/problem2/fancy-form/eslint.config.js

@@ -0,0 +1,23 @@
+import js from '@eslint/js'
+import globals from 'globals'
+import reactHooks from 'eslint-plugin-react-hooks'
+import reactRefresh from 'eslint-plugin-react-refresh'
+import tseslint from 'typescript-eslint'
+import { defineConfig, globalIgnores } from 'eslint/config'
+
+export default defineConfig([
+  globalIgnores(['dist']),
+  {
+    files: ['**/*.{ts,tsx}'],
+    extends: [
+      js.configs.recommended,
+      tseslint.configs.recommended,
+      reactHooks.configs.flat.recommended,
+      reactRefresh.configs.vite,
+    ],
+    languageOptions: {
+      ecmaVersion: 2020,
+      globals: globals.browser,
+    },
+  },
+])

src/problem2/fancy-form/index.html

@@ -0,0 +1,13 @@
+<!doctype html>
+<html lang="en">
+  <head>
+    <meta charset="UTF-8" />
+    <link rel="icon" type="image/svg+xml" href="/vite.svg" />
+    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
+    <title>fancy-form</title>
+  </head>
+  <body>
+    <div id="root"></div>
+    <script type="module" src="/src/main.tsx"></script>
+  </body>
+</html>

src/problem2/fancy-form/package.json

@@ -0,0 +1,41 @@
+{
+  "name": "fancy-form",
+  "private": true,
+  "version": "0.0.0",
+  "type": "module",
+  "scripts": {
+    "dev": "vite",
+    "build": "tsc -b && vite build",
+    "lint": "eslint .",
+    "preview": "vite preview"
+  },
+  "dependencies": {
+    "@tailwindcss/vite": "^4.2.1",
+    "class-variance-authority": "^0.7.1",
+    "clsx": "^2.1.1",
+    "lucide-react": "^0.576.0",
+    "radix-ui": "^1.4.3",
+    "react": "^19.2.0",
+    "react-dom": "^19.2.0",
+    "sonner": "^2.0.7",
+    "tailwind-merge": "^3.5.0",
+    "tailwindcss": "^4.2.1"
+  },
+  "devDependencies": {
+    "@eslint/js": "^9.39.1",
+    "@types/node": "^25.3.3",
+    "@types/react": "^19.2.7",
+    "@types/react-dom": "^19.2.3",
+    "@vitejs/plugin-react": "^5.1.1",
+    "babel-plugin-react-compiler": "^1.0.0",
+    "eslint": "^9.39.1",
+    "eslint-plugin-react-hooks": "^7.0.1",
+    "eslint-plugin-react-refresh": "^0.4.24",
+    "globals": "^16.5.0",
+    "shadcn": "^3.8.5",
+    "tw-animate-css": "^1.4.0",
+    "typescript": "~5.9.3",
+    "typescript-eslint": "^8.48.0",
+    "vite": "^7.3.1"
+  }
+}

src/problem2/fancy-form/src/App.tsx

@@ -0,0 +1,14 @@
+import { Toaster } from 'sonner'
+import { SwapCard } from './components/SwapCard'
+import './App.css'
+
+function App() {
+  return (
+    <div className="min-h-screen bg-gradient-to-br from-indigo-50 via-violet-50 to-purple-100 flex items-center justify-center p-4">
+      <SwapCard />
+      <Toaster position="top-center" richColors />
+    </div>
+  )
+}
+
+export default App

src/problem2/fancy-form/src/components/RateDisplay.tsx

@@ -0,0 +1,22 @@
+import type { Token } from '@/types/swap'
+
+interface RateDisplayProps {
+  fromToken: Token | null
+  toToken: Token | null
+  exchangeRate: number | null
+}
+
+export function RateDisplay({ fromToken, toToken, exchangeRate }: RateDisplayProps) {
+  if (!fromToken || !toToken || exchangeRate === null) return null
+
+  return (
+    <div className="flex items-center justify-center text-sm text-muted-foreground py-1">
+      <span>
+        1 {fromToken.symbol} ={' '}
+        <span className="text-foreground font-medium">
+          {String(parseFloat(exchangeRate.toFixed(6)))} {toToken.symbol}
+        </span>
+      </span>
+    </div>
+  )
+}

src/problem2/fancy-form/src/components/SubmitButton.tsx

@@ -0,0 +1,26 @@
+import { Loader2 } from 'lucide-react'
+import { Button } from '@/components/ui/button'
+
+interface SubmitButtonProps {
+  loading: boolean
+  disabled?: boolean
+}
+
+export function SubmitButton({ loading, disabled }: SubmitButtonProps) {
+  return (
+    <Button
+      type="submit"
+      disabled={loading || disabled}
+      className="w-full h-12 text-base font-semibold"
+    >
+      {loading ? (
+        <>
+          <Loader2 className="mr-2 h-5 w-5 animate-spin" />
+          Confirming...
+        </>
+      ) : (
+        'Confirm Swap'
+      )}
+    </Button>
+  )
+}

src/problem2/fancy-form/src/components/SwapButton.tsx

@@ -0,0 +1,29 @@
+import { useState } from 'react'
+import { ArrowUpDown } from 'lucide-react'
+
+interface SwapButtonProps {
+  onClick: () => void
+}
+
+export function SwapButton({ onClick }: SwapButtonProps) {
+  const [rotating, setRotating] = useState(false)
+
+  function handleClick() {
+    setRotating(true)
+    onClick()
+    setTimeout(() => setRotating(false), 300)
+  }
+
+  return (
+    <div className="flex justify-center -my-2 relative z-10">
+      <button
+        onClick={handleClick}
+        className="h-10 w-10 rounded-full bg-card border-2 border-border flex items-center justify-center hover:bg-muted transition-colors shadow-md"
+      >
+        <ArrowUpDown
+          className={`h-4 w-4 text-muted-foreground transition-transform duration-300 ${rotating ? 'rotate-180' : ''}`}
+        />
+      </button>
+    </div>
+  )
+}