diff --git a/lib/problems.rb b/lib/problems.rb
index 5085953d..3cc887c9 100644
--- a/lib/problems.rb
+++ b/lib/problems.rb
@@ -1,13 +1,40 @@
 require_relative './stack.rb'
 
-# Time Complexity: ?
-# Space Complexity: ?
+
+# Time Complexity: O(n)
+# Space Complexity: O(n)
 def balanced(string)
-  raise NotImplementedError, "Not implemented yet"
+  # raise NotImplementedError, "Not implemented yet"
+  return true if string.empty?
+
+  stack = Stack.new()
+
+  open = {
+    '(' => ')',
+    '{' => '}',
+    '[' => ']'
+  }
+
+  close = {
+    ')' => '(',
+    '}' => '{',
+    ']' => '['
+  }
+
+  string.each_char do |char|
+    if open[char]
+      stack.push(char)
+    elsif close[char] != stack.pop
+      return false
+    end
+  end
+
+  return stack.empty?
+  
 end
 
 # Time Complexity: ?
 # Space Complexity: ?
 def evaluate_postfix(postfix_expression)
-  raise NotImplementedError, "Not implemented yet"
+  # raise NotImplementedError, "Not implemented yet"
 end
diff --git a/lib/queue.rb b/lib/queue.rb
index 828217c6..34e5c110 100644
--- a/lib/queue.rb
+++ b/lib/queue.rb
@@ -1,31 +1,73 @@
 class Queue
 
+  MAX_SIZE = 20
+
   def initialize
     # @store = ...
-    raise NotImplementedError, "Not yet implemented"
+    # raise NotImplementedError, "Not yet implemented"
+    @store = Array.new(MAX_SIZE)
+    @front = -1
+    @rear = -1
   end
 
   def enqueue(element)
-    raise NotImplementedError, "Not yet implemented"
+    # 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 
+      @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"
+    # raise NotImplementedError, "Not yet implemented"
+    return nil if @store.empty?
+    raise ArgumentError.new("Queue is empty") if @front == -1
+    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"
+    # raise NotImplementedError, "Not yet implemented"
+    return @store[@front]
   end
 
   def size
-    raise NotImplementedError, "Not yet implemented"
+    # raise NotImplementedError, "Not yet implemented"
+    return 0 if @front == -1
+    return @front < @rear ? @rear - @front + 1 : MAX_SIZE - @front + @rear
   end
 
   def empty?
-    raise NotImplementedError, "Not yet implemented"
+    # raise NotImplementedError, "Not yet implemented"
+    return  @front == -1 
   end
 
   def to_s
-    return @store.to_s
+    # return @store.to_s
+    result = []
+    MAX_SIZE.times do |i|
+      index = ( i + @front) % MAX_SIZE
+      result << @store[index] if @store[index]
+    end
+    return result.to_s
   end
+
 end
diff --git a/lib/stack.rb b/lib/stack.rb
index cfc6ef0f..6b34fd7d 100644
--- a/lib/stack.rb
+++ b/lib/stack.rb
@@ -1,19 +1,25 @@
 class Stack
   def initialize
     # @store = ...
-    raise NotImplementedError, "Not yet implemented"
+    # raise NotImplementedError, "Not yet implemented"
+    @store = LinkedList.new
   end
 
   def push(element)
-    raise NotImplementedError, "Not yet implemented"
+    # raise NotImplementedError, "Not yet implemented"
+    @store.add_first(element)
   end
 
   def pop
-    raise NotImplementedError, "Not yet implemented"
+  #   raise NotImplementedError, "Not yet implemented"
+    return nil if self.empty?
+    item = @store.remove_first
+    return item
   end
 
   def empty?
-    raise NotImplementedError, "Not yet implemented"
+    # raise NotImplementedError, "Not yet implemented"
+    return @store.empty?
   end
 
   def to_s
diff --git a/test/problems_test.rb b/test/problems_test.rb
index 046f059e..1738b39f 100644
--- a/test/problems_test.rb
+++ b/test/problems_test.rb
@@ -1,8 +1,9 @@
 require_relative 'test_helper'
+require_relative '../lib/problems'
 
 Minitest::Reporters.use! Minitest::Reporters::SpecReporter.new
 
-xdescribe "Test wave 3 problems" do
+describe "Test wave 3 problems" do
   describe "balanced" do
     it "Given balanced strings it should return true" do
       
@@ -33,7 +34,7 @@
     end
   end
 
-  describe "postfix" do
+  xdescribe "postfix" do
     it "can add a 2 numbers together" do
       
       expect(evaluate_postfix("34+")).must_equal 7