diff --git a/lib/queue.rb b/lib/queue.rb
index 828217c6..75f06cb1 100644
--- a/lib/queue.rb
+++ b/lib/queue.rb
@@ -1,31 +1,76 @@
 class Queue
 
+  MAX_SIZE = 20
+
   def initialize
-    # @store = ...
-    raise NotImplementedError, "Not yet implemented"
+    @store = Array.new(MAX_SIZE)
+    @front = @rear = -1
   end
 
   def enqueue(element)
-    raise NotImplementedError, "Not yet implemented"
+    if (@front == 0 && @rear == MAX_SIZE - 1) || (@rear == (@front - 1) % (MAX_SIZE - 1))
+      raise ArgumentError.new("The queue is full")
+    elsif (@front == -1) && (@rear == -1)
+      @front = 0
+      @rear = 0
+    elsif @rear == MAX_SIZE - 1 && @front != 0
+      @rear = 0
+    else
+      @rear += 1
+    end
+
+    @store[@rear] = element
+
   end
 
   def dequeue
-    raise NotImplementedError, "Not yet implemented"
+    if @store.empty?
+      raise ArgumentError.new("the Queue is empty")
+    end
+  
+    data = @store[@front]
+
+    @store[@front] = nil
+    
+    if (@front == @rear)
+      @front == -1
+      @rear == -1 
+    elsif (@front == MAX_SIZE - 1) 
+      @front = 0
+    else 
+      @front += 1
+    end
+
+    return data
   end
 
   def front
-    raise NotImplementedError, "Not yet implemented"
+    return @store[@front]
   end
 
   def size
-    raise NotImplementedError, "Not yet implemented"
+    if @rear >= @front
+      return @rear - @front
+    else
+      MAX_SIZE - @front + @back
+    end
   end
 
   def empty?
-    raise NotImplementedError, "Not yet implemented"
+    return @front.nil? || @front == @rear
   end
 
   def to_s
-    return @store.to_s
+    queue = []
+
+    20.times do |i|
+      index = (i + @front) % MAX_SIZE
+      
+      if @store[index]
+        queue << @store[index]
+      end
+    end
+
+    return queue.to_s
   end
 end
diff --git a/lib/stack.rb b/lib/stack.rb
index cfc6ef0f..e875b92f 100644
--- a/lib/stack.rb
+++ b/lib/stack.rb
@@ -1,19 +1,21 @@
 class Stack
   def initialize
     # @store = ...
-    raise NotImplementedError, "Not yet implemented"
+    @store = LinkedList.new
   end
 
   def push(element)
-    raise NotImplementedError, "Not yet implemented"
+    @store.add_first(element)
   end
 
   def pop
-    raise NotImplementedError, "Not yet implemented"
+    return nil if @store.empty?
+
+    return @store.remove_first
   end
 
   def empty?
-    raise NotImplementedError, "Not yet implemented"
+    return @store.empty?
   end
 
   def to_s