refactor: use Set for findCommonItems to reduce from O(n*m) to O(n+m)

Author: marquinacarlos

Sprint-1/JavaScript/findCommonItems/findCommonItems.js

@@ -1,14 +1,25 @@
 /**
  * Finds common items between two arrays.
  *
- * Time Complexity:
- * Space Complexity:
- * Optimal Time Complexity:
+ * Time Complexity: O(n * m) - filter iterates firstArray, includes iterates secondArray
+ * Space Complexity: O(n) - Set and result array
+ * Optimal Time Complexity: O(n + m) - convert secondArray to Set for O(1) lookups
  *
  * @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 secondSet = new Set(secondArray);
+  const seen = new Set();
+  const result = [];
+
+  for (const item of firstArray) {
+    if (secondSet.has(item) && !seen.has(item)) {
+      seen.add(item);
+      result.push(item);
+    }
+  }
+
+  return result;
+};

Sprint-1/Python/find_common_items/find_common_items.py

@@ -9,13 +9,17 @@ def find_common_items(
     """
     Find common items between two arrays.
 
-    Time Complexity:
-    Space Complexity:
-    Optimal time complexity:
+    Time Complexity: O(n * m) - nested loops compare every pair
+    Space Complexity: O(n) - stores common items in list
+    Optimal time complexity: O(n + m) - convert second_sequence to set for O(1) lookups
     """
+    second_set = set(second_sequence)
+    seen = set()
     common_items: List[ItemType] = []
-    for i in first_sequence:
-        for j in second_sequence:
-            if i == j and i not in common_items:
-                common_items.append(i)
+
+    for item in first_sequence:
+        if item in second_set and item not in seen:
+            seen.add(item)
+            common_items.append(item)
+
     return common_items