diff --git a/lib/practice_exercises.rb b/lib/practice_exercises.rb
index 291e4e6..ad82519 100644
--- a/lib/practice_exercises.rb
+++ b/lib/practice_exercises.rb
@@ -1,13 +1,34 @@
 
-# Time Complexity: ?
-# Space Complexity: ?
+# Time Complexity: O(n^2)
+# Space Complexity: O(1)
 def remove_duplicates(list)
-  raise NotImplementedError, "Not implemented yet"
+  list.each do |i|
+    if list[i] == list[i + 1]
+      list.delete_at(i)
+    end
+  end
+  return list
 end
 
-# Time Complexity: ?
-# Space Complexity: ?
+# Time Complexity: O(n)
+# Space Complexity: O(1)
 def longest_prefix(strings)
-  raise NotImplementedError, "Not implemented yet"
+  loops = (strings.length) - 1
+  comparison_word = strings[0]
+  
+  loops.times do |i|
+    prefix = ""
+    counter = 0
+    
+    strings[i + 1].each_char do |letter|
+      if letter == comparison_word[counter]
+        prefix<<(letter)
+      end
+      counter += 1
+    end
+    comparison_word = prefix
+  end
+  
+  return comparison_word
 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