diff --git a/lib/practice_exercises.rb b/lib/practice_exercises.rb
index 291e4e6..086e881 100644
--- a/lib/practice_exercises.rb
+++ b/lib/practice_exercises.rb
@@ -1,13 +1,45 @@
+require "pry"
+# Time Complexity: ? O(n) where n corresponds with the length of input array
+# Space Complexity: ? O(1) not creating any additional space in memory here, just deleting in place
 
-# Time Complexity: ?
-# Space Complexity: ?
 def remove_duplicates(list)
-  raise NotImplementedError, "Not implemented yet"
+  if list.empty? || list.length == 1 
+    return list
+  else
+    i = 0
+    j = 1
+    until  list[j] == nil
+      if list[i] == list[j]
+        list.delete_at(i)
+      end
+      i += 1
+      j += 1
+    end
+    return list
+    # raise NotImplementedError, "Not implemented yet"
+  end
 end
 
-# Time Complexity: ?
+# time complexity: ?
 # Space Complexity: ?
+
+
 def longest_prefix(strings)
-  raise NotImplementedError, "Not implemented yet"
+  a = ""
+  collection_of_letters = strings.first[0]
+  j = 0
+  
+  strings.each_with_index do |string, i|
+    
+    return a if string[i][j] != collection_of_letters
+    if j == strings.length
+      
+      a << string[i][j]
+    end
+    j += 1
+  end
+  return a
+  # raise NotImplementedError, "Not implemented yet"
 end
 
+
diff --git a/test/practice_exercises_test.rb b/test/practice_exercises_test.rb
index 11d820b..f0e5f75 100644
--- a/test/practice_exercises_test.rb
+++ b/test/practice_exercises_test.rb
@@ -9,35 +9,44 @@
     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 Sabrina's strings" do
+    #   strings = [“flower”,“flower”,“flower”]
+    
+    #   output = longest_prefix(string)
+    
+    #   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
-end
+end
\ No newline at end of file