refactor remove_duplicates

Author: RihannaP

Sprint-1/Python/remove_duplicates/remove_duplicates.py

@@ -7,19 +7,16 @@ 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)
+    Space complexity: O(n)
+    Optimal time complexity: O(n)
     """
     unique_items = []
+    seen = set()
 
     for value in values:
-        is_duplicate = False
-        for existing in unique_items:
-            if value == existing:
-                is_duplicate = True
-                break
-        if not is_duplicate:
+        if value not in seen:
             unique_items.append(value)
+            seen.add(value)
 
     return unique_items