diff --git a/lib/practice_exercises.rb b/lib/practice_exercises.rb
index 291e4e6..3be46c7 100644
--- a/lib/practice_exercises.rb
+++ b/lib/practice_exercises.rb
@@ -1,13 +1,38 @@
 
-# Time Complexity: ?
-# Space Complexity: ?
+# Time Complexity: O(n)
+# Space Complexity: O(n)
 def remove_duplicates(list)
-  raise NotImplementedError, "Not implemented yet"
+  # go through each element in the array and remove duplicates
+  
+  if list.length == 1 || list[0] == nil
+    return list
+  end
+  
+  list.each_with_index do |item, i|
+    if item == list[i + 1]
+      list[i + 1] = nil 
+    end
+  end
+  
+  
+  return list
+  
 end
 
-# Time Complexity: ?
-# Space Complexity: ?
+# Time Complexity: O(n * m)
+# Space Complexity: O(1)
 def longest_prefix(strings)
-  raise NotImplementedError, "Not implemented yet"
+  
+  longest_prefix = ""
+  strings[0].length.times do |i|
+    char = strings[0][i]
+    strings.each_with_index do |string|
+      if string[i] != char || string[i] == nil
+        break
+      elsif char == string[i] && string == strings.last
+        longest_prefix += char
+      end
+    end
+  end
+  return longest_prefix
 end
-