function refactored and explained complexity

Author: RomanSanaye

Sprint-1/JavaScript/calculateSumAndProduct/calculateSumAndProduct.js

@@ -9,24 +9,24 @@
  *   "product": 30 // 2 * 3 * 5
  * }
  *
- * Time Complexity:
- * Space Complexity:
- * Optimal Time Complexity:
+ * Time Complexity: O(n) - one loop through the list (the original used two loops, 2n steps, which is also O(n)).
+ * Space Complexity: O(1) - only two variables (sum, product), regardless of input size
+ * Optimal Time Complexity: O(n) - every number must be read at least once, so we can't do better than linear time
+ *
+ * Refactor: the complexity can't be reduced, but merging the two loops into
+ * one makes the code cleaner and does half the steps.
  *
  * @param {Array<number>} numbers - Numbers to process
  * @returns {Object} Object containing running total and product
  */
 export function calculateSumAndProduct(numbers) {
   let sum = 0;
-  for (const num of numbers) {
-    sum += num;
-  }
-
   let product = 1;
   for (const num of numbers) {
+    sum += num;
     product *= num;
   }
-
+ 
   return {
     sum: sum,
     product: product,