feat: add iterative factorial algorithm

Maths/FactorialIterative.js

@@ -0,0 +1,24 @@
+/**
+ * @function factorialIterative
+ * @description Calculates the factorial of a non-negative integer
+ *   using an iterative approach. The factorial of n (n!) is the
+ *   product of all positive integers less than or equal to n.
+ * @param {number} n - A non-negative integer
+ * @returns {number} - The factorial of n
+ * @see https://en.wikipedia.org/wiki/Factorial
+ * @example factorialIterative(0) => 1
+ * @example factorialIterative(5) => 120
+ * @example factorialIterative(10) => 3628800
+ */
+const factorialIterative = (n) => {
+  if (!Number.isInteger(n) || n < 0) {
+    throw new TypeError('Input must be a non-negative integer')
+  }
+  let result = 1
+  for (let i = 2; i <= n; i++) {
+    result *= i
+  }
+  return result
+}
+
+export { factorialIterative }

Maths/test/FactorialIterative.test.js

@@ -0,0 +1,47 @@
+import { factorialIterative } from '../FactorialIterative.js'
+
+describe('factorialIterative', () => {
+  test('factorialIterative(0) returns 1', () => {
+    expect(factorialIterative(0)).toBe(1)
+  })
+
+  test('factorialIterative(1) returns 1', () => {
+    expect(factorialIterative(1)).toBe(1)
+  })
+
+  test('factorialIterative(2) returns 2', () => {
+    expect(factorialIterative(2)).toBe(2)
+  })
+
+  test('factorialIterative(3) returns 6', () => {
+    expect(factorialIterative(3)).toBe(6)
+  })
+
+  test('factorialIterative(5) returns 120', () => {
+    expect(factorialIterative(5)).toBe(120)
+  })
+
+  test('factorialIterative(7) returns 5040', () => {
+    expect(factorialIterative(7)).toBe(5040)
+  })
+
+  test('factorialIterative(10) returns 3628800', () => {
+    expect(factorialIterative(10)).toBe(3628800)
+  })
+
+  test('factorialIterative(12) returns 479001600', () => {
+    expect(factorialIterative(12)).toBe(479001600)
+  })
+
+  test('throws TypeError for negative input', () => {
+    expect(() => factorialIterative(-1)).toThrow(TypeError)
+  })
+
+  test('throws TypeError for float input', () => {
+    expect(() => factorialIterative(1.5)).toThrow(TypeError)
+  })
+
+  test('throws TypeError for string input', () => {
+    expect(() => factorialIterative('5')).toThrow(TypeError)
+  })
+})