diff --git a/lib/practice_exercises.rb b/lib/practice_exercises.rb
index 291e4e6..c1c15b8 100644
--- a/lib/practice_exercises.rb
+++ b/lib/practice_exercises.rb
@@ -1,13 +1,35 @@
 
-# Time Complexity: ?
-# Space Complexity: ?
+# Time Complexity: o(n)
+# Space Complexity: o(1)
 def remove_duplicates(list)
-  raise NotImplementedError, "Not implemented yet"
+  #raise NotImplementedError, "Not implemented yet"
+  array = list.length
+  index_1 = 0
+  array.times do
+    if list[index_1] == list[index_1 + 1]
+      list.delete_at(index_1)
+    else 
+      index_1 +=1
+    end
+  end 
+  return list
 end
 
-# Time Complexity: ?
-# Space Complexity: ?
+# Time Complexity: o(n^2)
+# Space Complexity: o(1)
 def longest_prefix(strings)
-  raise NotImplementedError, "Not implemented yet"
-end
+  # raise NotImplementedError, "Not implemented yet"
+  return "" unless (strings.length > 0)
+  output = ""
+  first_w = strings[0]
+  i = 0
+  first_w.each_char do |letter|
+    if strings.all?{|string| string[i] == letter }
+      
+      output += letter
+      i += 1
+    end
+  end
+  return output
+end