diff --git a/lib/practice_exercises.rb b/lib/practice_exercises.rb
index 291e4e6..8713dda 100644
--- a/lib/practice_exercises.rb
+++ b/lib/practice_exercises.rb
@@ -1,13 +1,44 @@
 
-# Time Complexity: ?
-# Space Complexity: ?
+# Time Complexity: O(n)
+# Space Complexity: O(n)
 def remove_duplicates(list)
-  raise NotImplementedError, "Not implemented yet"
+  item_list = []
+  list.each_with_index do |item|
+    if item_list.include?(item) == false
+      item_list << item
+    end
+  end
+  return item_list
 end
 
-# Time Complexity: ?
-# Space Complexity: ?
+# Time Complexity: O(n2)
+# Space Complexity: O(n)
 def longest_prefix(strings)
-  raise NotImplementedError, "Not implemented yet"
+  prefix = ""
+  count = 0
+  check = true
+  continue = true
+  strings[0].each_char do |character|
+    letter = character
+    strings.each do |string|
+      if string[count] != letter
+        continue = false
+        break
+      end
+    end
+    if continue == false
+      break
+    end
+    count +=1
+  end
+  if count == 0
+    return prefix
+  end
+  return prefix = strings[0][0..count-1]
 end
 
+
+
+
+
+
diff --git a/test/practice_exercises_test.rb b/test/practice_exercises_test.rb
index 4d0bc10..0aaabc9 100644
--- a/test/practice_exercises_test.rb
+++ b/test/practice_exercises_test.rb
@@ -9,34 +9,34 @@
     it "works for empty arrays" do
       expect(remove_duplicates([])).must_equal []
     end
-
+    
     it "will remove duplicates for longer arrays" do
       expect(remove_duplicates([1, 2, 2, 3, 3, 4]).reject{|num| num == nil }).must_equal [1, 2, 3, 4]
     end
   end
-
+  
   describe "Longest valid substring" do
     it "will work for the README strings" do
       strings = ["flower","flow","flight"]
-
+      
       output = longest_prefix(strings)
-
+      
       expect(output).must_equal "fl"
     end
-
+    
     it "will work for the strings with the common prefix in the rear" do
       strings = ["flower","flow","flight", "fpastafl"]
-
+      
       output = longest_prefix(strings)
-
+      
       expect(output).must_equal "f"
     end
-
+    
     it "will work for the README strings" do
       strings = ["dog","racecar","car"]
-
+      
       output = longest_prefix(strings)
-
+      
       expect(output).must_equal ""
     end
   end