feat: add multiplicative persistence algorithm

Maths/MultiplicativePersistence.js

@@ -0,0 +1,28 @@
+/**
+ * @function multiplicativePersistence
+ * @description Multiplicative persistence is the number of times you must
+ *   multiply the digits of a number until you reach a single digit.
+ *   For example, 39: 3×9=27, 2×7=14, 1×4=4 — persistence is 3.
+ * @param {number} n - A non-negative integer
+ * @returns {number} - The multiplicative persistence of n
+ * @see https://en.wikipedia.org/wiki/Persistence_of_a_number
+ * @example multiplicativePersistence(39) => 3
+ * @example multiplicativePersistence(999) => 4
+ * @example multiplicativePersistence(4) => 0
+ */
+const multiplicativePersistence = (n) => {
+  if (!Number.isInteger(n) || n < 0) {
+    throw new TypeError('Input must be a non-negative integer')
+  }
+  let count = 0
+  let current = n
+  while (current >= 10) {
+    current = String(current)
+      .split('')
+      .reduce((product, d) => product * Number(d), 1)
+    count++
+  }
+  return count
+}
+
+export { multiplicativePersistence }

Maths/test/MultiplicativePersistence.test.js

@@ -0,0 +1,51 @@
+import { multiplicativePersistence } from '../MultiplicativePersistence.js'
+
+describe('multiplicativePersistence', () => {
+  test('single digit returns 0', () => {
+    expect(multiplicativePersistence(4)).toBe(0)
+  })
+
+  test('multiplicativePersistence(10) returns 1', () => {
+    expect(multiplicativePersistence(10)).toBe(1)
+  })
+
+  test('multiplicativePersistence(25) returns 2', () => {
+    expect(multiplicativePersistence(25)).toBe(2)
+  })
+
+  test('multiplicativePersistence(39) returns 3', () => {
+    expect(multiplicativePersistence(39)).toBe(3)
+  })
+
+  test('multiplicativePersistence(77) returns 4', () => {
+    expect(multiplicativePersistence(77)).toBe(4)
+  })
+
+  test('multiplicativePersistence(999) returns 4', () => {
+    expect(multiplicativePersistence(999)).toBe(4)
+  })
+
+  test('multiplicativePersistence(0) returns 0', () => {
+    expect(multiplicativePersistence(0)).toBe(0)
+  })
+
+  test('multiplicativePersistence(1) returns 0', () => {
+    expect(multiplicativePersistence(1)).toBe(0)
+  })
+
+  test('multiplicativePersistence(100) returns 1', () => {
+    expect(multiplicativePersistence(100)).toBe(1)
+  })
+
+  test('throws TypeError for negative input', () => {
+    expect(() => multiplicativePersistence(-39)).toThrow(TypeError)
+  })
+
+  test('throws TypeError for float input', () => {
+    expect(() => multiplicativePersistence(3.9)).toThrow(TypeError)
+  })
+
+  test('throws TypeError for string input', () => {
+    expect(() => multiplicativePersistence('39')).toThrow(TypeError)
+  })
+})