feat(armstrong): add 'armstrong' option (#244)

* feat(armstrong): add 'armstrong' option

* Update index.js

* Update index.js

Author: yeohsoonkeat

src/armstrong.js

@@ -0,0 +1,25 @@
+export default armstrong
+
+/**
+ * This method will check if a number is an armstrong number.
+ * @param {Number} num number to check
+ * @return{Boolean} True or false
+ */
+
+function armstrong(num) {
+  let eachDigit = 0
+  let check = 0
+  let digit = 0
+  for (let i = num; i > 0; i = Math.floor(i / 10)) {
+    digit = digit + 1
+  }
+  for (let i = num; i > 0; i = Math.floor(i / 10)) {
+    eachDigit = i % 10
+    check = check + Math.pow(eachDigit, digit)
+  }
+  if (check === num) {
+    return true
+  } else {
+    return false
+  }
+}

src/index.js

@@ -92,6 +92,7 @@ import removeElementByIndex from './removeElementByIndex'
 import clone from './clone'
 import arrMultiply from './array-multiplier'
 import second from './second'
+import armstrong from './armstrong'
 
 export {
   reverseArrayInPlace,
@@ -188,4 +189,5 @@ export {
   clone,
   arrMultiply,
   second,
+  armstrong,
 }

test/armstrong.test.js

@@ -0,0 +1,16 @@
+import test from 'ava'
+import {armstrong} from '../src'
+
+test('This number is not an armstrong number', t => {
+  const object = 123
+  const expected = false
+  const actual = armstrong(object)
+  t.deepEqual(actual, expected)
+})
+
+test('This number is an armstrong number', t => {
+  const object = 371
+  const expected = true
+  const actual = armstrong(object)
+  t.deepEqual(actual, expected)
+})