Add step2-01 final folder with solutions

step2-01/final/src/fibonacci.ts

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+export function fib(n: number) {
+  return n <= 1 ? n : fib(n - 1) + fib(n - 2);
+}
+
+const FibConst: number = 3;
+export default FibConst;

step2-01/final/src/index.ts

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+import FibConst, { fib } from './fibonacci';
+import { Stack } from './stack';
+
+console.log('hello world');
+
+// ---- Modules ----
+console.log('fib(FibConst) is:', fib(FibConst));
+
+// ---- Types and Interfaces ----
+type TrafficLight = 'red' | 'green' | 'yellow';
+const annoyingLight: TrafficLight = 'red';
+
+interface Car {
+  wheels: number;
+  color: string;
+  make: string;
+  model: string;
+}
+
+const myCar: Car = {
+  wheels: 4,
+  color: 'blue',
+  make: 'Toyota',
+  model: 'Camry'
+};
+// JSON.stringify makes a nice string representation of an object
+console.log('My car:', JSON.stringify(myCar));
+
+// ---- Generics ----
+const myStack = new Stack<number>();
+myStack.push(1);
+myStack.push(2);
+myStack.push(3);
+console.log('Number on top of the stack:', myStack.pop());
+
+// ---- Spread and Destructuring ----
+const obj1 = {
+  first: 'who',
+  second: 'what',
+  third: 'dunno',
+  left: 'why'
+};
+
+const obj2 = {
+  center: 'because',
+  pitcher: 'tomorrow',
+  catcher: 'today'
+};
+
+const megaObj = { ...obj1, ...obj2 };
+
+const { first, second, catcher } = megaObj;
+console.log('First:', first);
+console.log('Second:', second);
+console.log('Catcher:', catcher);
+
+// ---- Async / Await ----
+function makePromise(): Promise<number> {
+  return Promise.resolve(5);
+}
+
+async function getGreeting(name: string): Promise<string> {
+  return 'hello ' + name;
+}
+
+async function run() {
+  const result = await makePromise();
+  console.log('makePromise returned:', result);
+
+  const greeting = await getGreeting('Ken');
+  console.log('greeting:', greeting);
+}
+
+run();
+
+// Make this file a module so its code doesn't go in the global scope
+export {};

step2-01/final/src/stack.ts

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+export class Stack<T> {
+  private _store: T[];
+
+  constructor() {
+    this._store = [];
+  }
+
+  push(elem: T): void {
+    this._store.push(elem);
+  }
+
+  pop(): T {
+    return this._store.pop();
+  }
+}