diff --git a/lib/practice_exercises.rb b/lib/practice_exercises.rb
index 291e4e6..eda0483 100644
--- a/lib/practice_exercises.rb
+++ b/lib/practice_exercises.rb
@@ -1,13 +1,89 @@
 
-# Time Complexity: ?
-# Space Complexity: ?
+# Time Complexity: O(n)
+# Space Complexity: O(n)
 def remove_duplicates(list)
-  raise NotImplementedError, "Not implemented yet"
+  # list is a sorted array of numbers
+  unique_list = []
+  
+  list.each do |element|
+    unless unique_list[-1] == element
+      unique_list << element
+    end
+  end
+  
+  return unique_list
 end
 
-# Time Complexity: ?
-# Space Complexity: ?
+
+
+
+# Time Complexity: O(n^2)
+# Space Complexity: O(n)
 def longest_prefix(strings)
-  raise NotImplementedError, "Not implemented yet"
+  shortest_string = strings.min_by { |string| string.length}  # O(n)
+  
+  match = ""
+  shortest_string.length.times do |index|   #O(n)
+    curr_char = strings[0][index]
+    
+    strings.each do |string|  #O(n)
+      if string[index] != curr_char
+        return match
+      end
+    end
+    
+    # all strings have matching letter on this index position
+    match << curr_char
+  end
+  
+  return match
 end
 
+
+
+
+
+#### ALTERNATE METHOD, THOUGHT I COULD DO BETTER THAN O(n^2) BUT COULDN'T ####
+
+# def longest_prefix_ALT(strings)
+#   # find the longest common prefix string amongst an array of strings
+#   # Time O(n^2) and Space O(n)
+
+#   # get the match results from the first 2 strings 
+#   prev_match = get_head_matches(strings[0], strings[1])
+
+#   # if the first 2 strings don't have any chars in common, answer is automatically ""
+#   if prev_match == ""
+#     return ""
+#   end
+
+#   # compare the prev_match with each subsequent string, modifying prev_match with each iteration
+#   ((strings.length)-2).times do |index|
+#     prev_match = get_head_matches(prev_match, strings[index+2])
+#     puts
+#   end
+
+#   return prev_match
+# end
+
+# def get_head_matches(string1, string2)    
+#   # O(n) time & O(1) space
+#   shorter_string = [string1, string2].min_by { |str| str.length }
+
+#   index = 0
+#   match = ""
+
+#   while index < shorter_string.length
+#     if string1[index] == string2[index]
+#       match << string1[index]
+#     else 
+#       break
+#     end
+
+#     index += 1
+#   end
+
+#   return match
+# end
+
+