diff --git a/lib/practice_exercises.rb b/lib/practice_exercises.rb
index 291e4e6..55d72e0 100644
--- a/lib/practice_exercises.rb
+++ b/lib/practice_exercises.rb
@@ -1,13 +1,43 @@
+require "pry"
+# Given nums = [0,0,1,1,1,2,2,3,3,4]
+# Your function should return length = 5, 
+# with the first five elements of nums being modified to 0, 1, 2, 3, and 4 respectively.
 
-# Time Complexity: ?
-# Space Complexity: ?
+# Time Complexity: O(n) - depends of the length of the list
+# Space Complexity: O(1) - doens't create another array
 def remove_duplicates(list)
-  raise NotImplementedError, "Not implemented yet"
-end
+  i = 0
+  while i < list.length
+    if list[i] == list[i+1]
+      list.delete_at(i)
+    end
+    i += 1
+  end  
+  return list
+end 
+
+# Find the longest common prefix string amongst an array of strings.
+# Input: ["flower","flow","flight"]
+# Output: "fl" 
+# Input: ["dog","racecar","car"]
+# Output: ""
 
-# Time Complexity: ?
-# Space Complexity: ?
+# Time Complexity: O(nm) - depends on the length of strings = n and length of string[0] = m
+# Space Complexity: O(m) - is reacreting a result total
 def longest_prefix(strings)
-  raise NotImplementedError, "Not implemented yet"
+  result = ""
+  i = 0
+  
+  strings[0].each_char do |letter|
+    strings.each do |string|
+      if letter != string[i]
+        return result
+      end
+    end
+    
+    result += letter
+    i += 1
+  end
+  
+  return result 
 end
-