merge: WhileLoopFactorial: Optimize and add tests (TheAlgorithms#992)

* Optimised the factorial function.

There was previously an unnecessary check for if the number was 0 or 1.

* Create WhileLoopFactorial.test.js

The test was not present previously.

* result *= num

* Update WhileLoopFactorial.test.js

* testFactorial function

* Space for formatting.

* should fix the formatting issues. I was having trouble with npx standard, so I just used the online verifier at https://standardjs.com/demo.html

Author: merelymyself

Maths/WhileLoopFactorial.js

@@ -1,15 +1,13 @@
 /*
-    author: Theepag
+    author: Theepag, optimised by merelymyself
  */
 export const factorialize = (num) => {
-  // Step 1. variable result to store num
-  let result = num
-  // If num = 0 OR 1, the factorial will return 1
-  if (num === 0 || num === 1) { return 1 }
+  // Step 1. Handles cases where num is 0 or 1, by returning 1.
+  let result = 1
   // Step 2. WHILE loop
   while (num > 1) {
+    result *= num // or result = result * num;
     num-- // decrement 1 at each iteration
-    result = result * num // or result = result * num;
   }
   // Step 3. Return the factorial
   return result

Maths/test/WhileLoopFactorial.test.js

@@ -0,0 +1,12 @@
+import { factorialize } from '../WhileLoopFactorial'
+
+function testFactorial (n, expected) {
+  test('Testing on ' + n + '!', () => {
+    expect(factorialize(n)).toBe(expected)
+  })
+}
+
+testFactorial(3, 6)
+testFactorial(7, 5040)
+testFactorial(0, 1)
+testFactorial(12, 479001600)