algorithm: check if number is Armstrong number (#44)

Author: SpiderMath

Maths/ArmstrongNumber.ts

@@ -0,0 +1,29 @@
+/** 
+ * @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
+  let cloneNum = num
+  const numOfDigits = Math.floor(1 + Math.log10(num))
+
+  while (cloneNum > 0) {
+    compNum += Math.pow(cloneNum % 10, numOfDigits)
+    cloneNum = Math.floor(cloneNum / 10)
+  }
+
+  return compNum === num
+}

Maths/test/ArmstrongNumber.test.ts

@@ -0,0 +1,5 @@
+import { ArmstrongNumber } from "../ArmstrongNumber"
+
+test.each([[9, true], [-310, false], [0, false], [407, true], [420, false], [92727, true], [13579, false]])('i is an Armstrong number or not', (num, expected) => {
+  expect(ArmstrongNumber(num)).toBe(expected)
+})