//栈
class Stack {
 var stack: [AnyObject]
 
 init() {
 stack = [AnyObject]()
 }
 
 func push(object: AnyObject) {
 stack.append(object)
 }
 
 func pop() -> AnyObject? {
 if !isEmpty() {
 return stack.removeLast()
 } else {
 return nil
 }
 }
 
 func isEmpty() -> Bool {
 return stack.isEmpty
 }
 
 func peek() -> AnyObject? {
 return stack.last
 }
 
 func size() -> Int {
 return stack.count
 }
}
 
//队列
class Queue {
 var queue: [AnyObject]
 
 init() {
 queue = [AnyObject]()
 }
 
 func enqueue(object: AnyObject) {
 queue.append(object)
 }
 
 func dequeue() -> AnyObject? {
 if !isEmpty() {
 return queue.removeFirst()
 } else {
 return nil
 
 }
 }
 
 func isEmpty() -> Bool {
 return queue.isEmpty
 }
 
 func peek() -> AnyObject? {
 return queue.first
 }
 
 func size() -> Int {
 return queue.count
 }
 
}