Refactor JavaScript array utilities to improve time complexity

Author: PratiAmalden

Sprint-1/JavaScript/calculateSumAndProduct/calculateSumAndProduct.js

@@ -9,26 +9,24 @@
  *   "product": 30 // 2 * 3 * 5
  * }
  *
- * Time Complexity:
- * Space Complexity:
- * Optimal Time Complexity:
+ *  Areas of inefficiency in original version:
+ * - Two separate passes over the array
+ * 
+ * Time Complexity: O(n)
+ * Space Complexity: O(1)
+ * Optimal Time Complexity: O(n) 
  *
  * @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,
-  };
-}
+  return { sum, product };
+}

Sprint-1/JavaScript/findCommonItems/findCommonItems.js

@@ -1,14 +1,27 @@
 /**
  * Finds common items between two arrays.
  *
- * Time Complexity:
- * Space Complexity:
- * Optimal Time Complexity:
+ * Areas of inefficiency in original version:
+ * - `secondArray.includes(item)` is O(m) and was called for each item in firstArray (n)
+ *   resulting in O(n * m) worst-case time.
+ *
+ * Time Complexity: O(n + m) average
+ * Space Complexity:  O(m + k) where:
+ * - m = secondArray length (Set storage)
+ * - k = number of unique common items (result Set storage)
+ * Optimal Time Complexity:  O(n + m)
  *
  * @param {Array} firstArray - First array to compare
  * @param {Array} secondArray - Second array to compare
  * @returns {Array} Array containing unique common items
  */
-export const findCommonItems = (firstArray, secondArray) => [
-  ...new Set(firstArray.filter((item) => secondArray.includes(item))),
-];
+export const findCommonItems = (firstArray, secondArray) => {
+  const setB = new Set(secondArray);
+  const common = new Set();
+
+  for (const item of firstArray) {
+    if (setB.has(item)) common.add(item);
+  }
+
+  return [...common];
+};

Sprint-1/JavaScript/hasPairWithSum/hasPairWithSum.js

@@ -1,21 +1,33 @@
 /**
  * Find if there is a pair of numbers that sum to a given target value.
+ *  
+ * Areas of inefficiency in original version:
+ * - Nested loops compare every possible pair.
+ * - This results in quadratic time complexity as input size grows.
+ * 
+ * Time Complexity: O(n²)
+ * Space Complexity: O(1)
+ * Optimal Time Complexity: O(n)
  *
- * Time Complexity:
- * Space Complexity:
- * Optimal Time Complexity:
- *
+ * - Use a Set to track numbers seen so far.
+ * - For each number x, check whether (target - x) has already been seen.
+ * 
  * @param {Array<number>} numbers - Array of numbers to search through
  * @param {number} target - Target sum to find
  * @returns {boolean} True if pair exists, false otherwise
  */
 export function hasPairWithSum(numbers, target) {
-  for (let i = 0; i < numbers.length; i++) {
-    for (let j = i + 1; j < numbers.length; j++) {
-      if (numbers[i] + numbers[j] === target) {
-        return true;
-      }
+  const seen = new Set();
+
+  for (const num of numbers) {
+    const complement = target - num;
+
+    if (seen.has(complement)) {
+      return true;
     }
+
+    seen.add(num);
   }
+
   return false;
-}
+}

Sprint-1/JavaScript/removeDuplicates/removeDuplicates.mjs

@@ -1,34 +1,25 @@
 /**
  * Remove duplicate values from a sequence, preserving the order of the first occurrence of each value.
  *
- * Time Complexity:
- * Space Complexity:
+ * Areas of inefficiency in original version:
+ * - Nested loop: for each element in inputSequence, it scanned uniqueItems so far.
+ *   That creates quadratic behavior in the worst case.
+ * 
+ * Time Complexity: O(n²)
+ * Space Complexity:O(n)
  * Optimal Time Complexity:
  *
  * @param {Array} inputSequence - Sequence to remove duplicates from
  * @returns {Array} New sequence with duplicates removed
  */
 export function removeDuplicates(inputSequence) {
+  const seen = new Set();
   const uniqueItems = [];
 
-  for (
-    let currentIndex = 0;
-    currentIndex < inputSequence.length;
-    currentIndex++
-  ) {
-    let isDuplicate = false;
-    for (
-      let compareIndex = 0;
-      compareIndex < uniqueItems.length;
-      compareIndex++
-    ) {
-      if (inputSequence[currentIndex] === uniqueItems[compareIndex]) {
-        isDuplicate = true;
-        break;
-      }
-    }
-    if (!isDuplicate) {
-      uniqueItems.push(inputSequence[currentIndex]);
+  for (const item of inputSequence) {
+    if (!seen.has(item)) {
+      seen.add(item);
+      uniqueItems.push(item);
     }
   }