feat: oct 21

ts/oct21/collatz.ts

···
+export const collatz = (n: number): number[] => {
+    if (n <= 0) throw new Error("Input must be a positive integer");
+    if (n === 2) return [2, 1];
+    if (n % 2 === 0) return [n, ...collatz(n / 2)];
+    return [n, ...collatz(3 * n + 1)];
+};

ts/oct21/evenDigits.ts

···
+export const evenDigits = (n: number): boolean => {
+    while (n > 0) {
+        const digit = n % 10;
+        if (digit % 2 !== 0) return false;
+        n = Math.floor(n / 10);
+    }
+    return true;
+};

ts/oct21/fizzBuzz.ts

···
+export const fizzBuzz = (n: number): string => {
+    if (n % 3 === 0 && n % 5 === 0) return "fizzBuzz";
+    if (n % 3 === 0) return "fizz";
+    if (n % 5 === 0) return "buzz";
+    return n.toString();
+};

ts/oct21/index.test.ts

···
+import { expect, test } from "bun:test";
+
+import { fizzBuzz } from "./fizzBuzz";
+import { collatz } from "./collatz";
+import { evenDigits } from "./evenDigits";
+
+test("FizzBuzz", () => {
+    expect(fizzBuzz(1)).toBe("1");
+    expect(fizzBuzz(3)).toBe("fizz");
+    expect(fizzBuzz(5)).toBe("buzz");
+    expect(fizzBuzz(15)).toBe("fizzBuzz");
+});
+
+test("Collatz", () => {
+    expect(collatz(3)).toEqual([3, 10, 5, 16, 8, 4, 2, 1]);
+    expect(collatz(1)).toEqual([1, 4, 2, 1]);
+    expect(collatz(4)).toEqual([4, 2, 1]);
+});
+
+test("All Even Digits", () => {
+    expect(evenDigits(2486)).toBe(true);
+    expect(evenDigits(1234)).toBe(false);
+});