feat: add Disarium number algorithm

Maths/DisariumNumber.js

@@ -0,0 +1,22 @@
+/**
+ * @function isDisariumNumber
+ * @description A Disarium number is a number where the sum of its digits
+ *   powered with their respective positions is equal to the number itself.
+ *   For example, 135: 1¹ + 3² + 5³ = 1 + 9 + 125 = 135.
+ * @param {number} n - A positive integer
+ * @returns {boolean} - True if n is a Disarium number, false otherwise
+ * @see https://en.wikipedia.org/wiki/Disarium_number
+ * @example isDisariumNumber(135) => true
+ * @example isDisariumNumber(89) => true
+ * @example isDisariumNumber(10) => false
+ */
+const isDisariumNumber = (n) => {
+  if (!Number.isInteger(n) || n < 1) {
+    throw new TypeError('Input must be a positive integer')
+  }
+  const digits = String(n).split('')
+  const sum = digits.reduce((acc, d, i) => acc + Math.pow(Number(d), i + 1), 0)
+  return sum === n
+}
+
+export { isDisariumNumber }

Maths/test/DisariumNumber.test.js

@@ -0,0 +1,51 @@
+import { isDisariumNumber } from '../DisariumNumber.js'
+
+describe('isDisariumNumber', () => {
+  test('1 is a Disarium number (1¹=1)', () => {
+    expect(isDisariumNumber(1)).toBe(true)
+  })
+
+  test('2 is a Disarium number (2¹=2)', () => {
+    expect(isDisariumNumber(2)).toBe(true)
+  })
+
+  test('89 is a Disarium number (8¹+9²=8+81=89)', () => {
+    expect(isDisariumNumber(89)).toBe(true)
+  })
+
+  test('135 is a Disarium number (1¹+3²+5³=1+9+125=135)', () => {
+    expect(isDisariumNumber(135)).toBe(true)
+  })
+
+  test('175 is a Disarium number', () => {
+    expect(isDisariumNumber(175)).toBe(true)
+  })
+
+  test('518 is a Disarium number', () => {
+    expect(isDisariumNumber(518)).toBe(true)
+  })
+
+  test('10 is NOT a Disarium number', () => {
+    expect(isDisariumNumber(10)).toBe(false)
+  })
+
+  test('12 is NOT a Disarium number', () => {
+    expect(isDisariumNumber(12)).toBe(false)
+  })
+
+  test('100 is NOT a Disarium number', () => {
+    expect(isDisariumNumber(100)).toBe(false)
+  })
+
+  test('throws TypeError for zero', () => {
+    expect(() => isDisariumNumber(0)).toThrow(TypeError)
+  })
+
+  test('throws TypeError for negative input', () => {
+    expect(() => isDisariumNumber(-135)).toThrow(TypeError)
+  })
+
+  test('throws TypeError for float input', () => {
+    expect(() => isDisariumNumber(13.5)).toThrow(TypeError)
+  })
+})