Refactor: optimize to O(n) using set while preserving order

Author: AFatmaa

Sprint-1/Python/remove_duplicates/remove_duplicates.py

@@ -7,19 +7,24 @@ def remove_duplicates(values: Sequence[ItemType]) -> List[ItemType]:
     """
     Remove duplicate values from a sequence, preserving the order of the first occurrence of each value.
 
-    Time complexity:
-    Space complexity:
-    Optimal time complexity:
+    Time complexity: O(n)
+    The old code checked the list repeatedly, which is O(n^2).
+    I used a 'Set' to remember seen items for O(1) lookups, while appending to a list to keep the order.
+
+    Space Complexity: O(n) - We use a Set to store seen items and a List for the result.
+
+    Optimal time complexity: O(n) - We must iterate through the input at least once.
     """
+
+    # Refactor: I used a Set to track items we have seen because checking a Set is O(1).
+    # I also used a List to build the result so we keep the original order.
+    seen = set()
     unique_items = []
 
     for value in values:
-        is_duplicate = False
-        for existing in unique_items:
-            if value == existing:
-                is_duplicate = True
-                break
-        if not is_duplicate:
+        # Check if we have seen this value before.
+        if value not in seen:
             unique_items.append(value)
+            seen.add(value)
 
     return unique_items