algorithm: check if number is Armstrong number

Maths/ArmstrongNumber.ts

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+/** 
+ * @function ArmstrongNumber
+ * @description Check if the provided number is an Armstrong number or not.
+ * @summary Armstrong numbers are numbers, the sum of whose digits each raised
+ * to the power of the number of digits is equal to the number itself.
+ * For example:
+ * 370 is an Armstrong number since 3^3 + 7^3 + 0^3 = 370
+ * (These numbers are also known as Narcissistic numbers, and Pluperfect numbers)
+ * @param {number} num The number you want to check for
+ * @return {boolean} Whether the input number is an Armstrong number
+ * @see [Wikipedia](https://en.wikipedia.org/wiki/Armstrong_number)
+ * @see [OEIS](https://oeis.org/A005188)
+ * @example ArmstrongNumber(370) = true
+ * @example ArmstrongNumber(10) = false
+ */
+export const ArmstrongNumber = (num: number): boolean => {
+  if (typeof num !== 'number' || num <= 0) return false;
+
+  let compNum = 0
+
+  const digitArr = num
+    .toString()
+    .split('');
+
+  digitArr.map((digit) => compNum += Math.pow(Number(digit), digitArr.length))
+
+  return num === compNum
+}

Maths/test/ArmstrongNumber.test.ts

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+import { ArmstrongNumber } from "../ArmstrongNumber"
+
+describe('ArmstrongNumber', () => {
+	it('should return the correct value', () => {
+		expect(ArmstrongNumber(9)).toBe(true)
+	})
+	it('should return the correct value', () => {
+		expect(ArmstrongNumber(-310)).toBe(false)
+	})
+	it('should return the correct value', () => {
+		expect(ArmstrongNumber(407)).toBe(true)
+	})
+	it('should return the correct value', () => {
+		expect(ArmstrongNumber(420)).toBe(false)
+	})
+	it('should return the correct value', () => {
+		expect(ArmstrongNumber(0)).toBe(false)
+	})
+
+	it('should return the correct value', () => {
+		expect(ArmstrongNumber(13579)).toBe(false)
+	})
+
+	it('should return the correct value', () => {
+		expect(ArmstrongNumber(92727)).toBe(true)
+	})
+})