diff --git a/lib/practice_exercises.rb b/lib/practice_exercises.rb
index 291e4e6..5cf6354 100644
--- a/lib/practice_exercises.rb
+++ b/lib/practice_exercises.rb
@@ -1,13 +1,34 @@
 
-# Time Complexity: ?
-# Space Complexity: ?
+# Time Complexity: O(n) where n is the sorted array
+# Space Complexity: O(1)
 def remove_duplicates(list)
-  raise NotImplementedError, "Not implemented yet"
+  counter = 0
+  list.length.times do |num|
+    if list[counter] == list[counter + 1]
+      list.delete_at(counter + 1)
+    else  
+      counter += 1
+    end
+  end
+  return list
 end
 
-# Time Complexity: ?
-# Space Complexity: ?
+# Time Complexity: O(n) where n is the strings array
+# Space Complexity: O(1)
 def longest_prefix(strings)
-  raise NotImplementedError, "Not implemented yet"
+  longest_prefix = strings[0]
+  strings.each do |string|
+    letter_counter = 0
+    longest_prefix.length.times do
+      if longest_prefix[letter_counter] == string[letter_counter]
+        letter_counter += 1
+      else 
+        longest_prefix = longest_prefix.slice(0, letter_counter)
+        break
+      end
+    end
+  end
+  return longest_prefix
 end
 
+
diff --git a/test/practice_exercises_test.rb b/test/practice_exercises_test.rb
index 11d820b..fc16b47 100644
--- a/test/practice_exercises_test.rb
+++ b/test/practice_exercises_test.rb
@@ -9,34 +9,43 @@
     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])).must_equal [1, 2, 3, 4]
+      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 that are the same" do 
+      strings = ["flower","flower","flower"]
+      
+      output = longest_prefix(strings)
+      
+      expect(output).must_equal "flower"
+    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