diff --git a/lib/practice_exercises.rb b/lib/practice_exercises.rb
index 291e4e6..d8b048c 100644
--- a/lib/practice_exercises.rb
+++ b/lib/practice_exercises.rb
@@ -1,13 +1,45 @@
 
-# Time Complexity: ?
-# Space Complexity: ?
+# Time Complexity: O(n^2)
+# Space Complexity: O(1)
 def remove_duplicates(list)
-  raise NotImplementedError, "Not implemented yet"
+  length = list.length
+  if length == 0
+    return []
+  end 
+  (1...length).each do |k|
+    if list[k] == list[k-1]
+      i = k
+      until i > length || list[i-1] == nil do 
+        list[i - 1] = list[i]
+        i += 1
+      end 
+    end
+    k += 1 
+  end 
+  return list
 end
 
-# Time Complexity: ?
-# Space Complexity: ?
+# Time Complexity: O(n), where n is total length of all strings combined 
+# Space Complexity: O(1)
 def longest_prefix(strings)
-  raise NotImplementedError, "Not implemented yet"
-end
-
+  strings.each do |string|
+    if string.length == 0
+      return ""
+    end 
+  end 
+  prefix = strings[0]
+  (1...strings.length).each do |n|
+    (0...prefix.length).each do |i|
+      if strings[n][i] != prefix[i]
+        if i == 0
+          prefix = ""
+          break
+        else 
+          prefix = prefix[0...i]
+          break
+        end 
+      end 
+    end 
+  end 
+  return prefix
+end 
\ No newline at end of file