Refactor remove_duplicates to use a set for O(n) removal of duplicates

Author: Fatma Degirmenci

Sprint-1/Python/remove_duplicates/remove_duplicates.py

@@ -7,19 +7,14 @@ 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: Outer loop O(n) Inner loop (worst case) O(n) total --->O(n*n)
+    Space complexity: We have an array ,unique_items, total --->O(n)
+    Optimal time complexity: O(n) using a set for fast lookups
     """
     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:
-            unique_items.append(value)
-
+    seen = set()
+    for value in values: # O(n)
+        if value not in seen: # O(1)
+            seen.add(value) # O(1)
+            unique_items.append(value) # O(1)
     return unique_items