LinkedList0.swift

class LinkedList<T> {
    
    public typealias Node = LLNode<T>
    
    private var head: Node?
    private var tail: Node?
    
    var isEmpty: Bool {
        return head == nil
    }
    
    var first: Node? {
        return head
    }
    
    var last: Node? {
        return tail
    }
    
    func append(value: T) {
        let newNode = Node(value: value)
        if let lastNode = last {
            newNode.previous = lastNode
            lastNode.next = newNode
        } else {
            head = newNode
        }
    }
}