Binary Tree in Swift 2.0.

BinaryTree.swift

//: Binary Tree

protocol CollectionTypeConvertible {
    typealias T
    var array: [T] { get }
}

class Node<T: Comparable> {
    let value: T
    var left: Node?
    var right: Node?

    convenience init(value: T) {
        self.init(value: value, left: nil, right: nil)
    }

    init(value: T, left: Node?, right: Node?) {
        self.value = value
        self.left = left
        self.right = right
    }

    func add(value: T) {
        if value < self.value {
            Node.addNode(&left, value: value)
        } else {
            Node.addNode(&right, value: value)
        }
    }

    static func addNode(inout node: Node?, value: T) {
        if node != nil {
            node!.add(value)
        } else {
            node = Node(value: value)
        }
    }
}

extension Node: CustomStringConvertible {
    var description: String {
        if left != nil && right != nil {
            return "\(value) => [left: \(left!), right: \(right!)]"
        } else if left != nil && right == nil {
            return "\(value) => [left: \(left!), right:]"
        } else if left == nil && right != nil {
            return "\(value) => [left:, right: \(right!)]"
        } else {
            return "\(value)"
        }
    }

    func draw() {
        left?.draw("", "    ", " |  ")
        print("\(value)")
        right?.draw("", " |  ", "    ")
    }

    func draw(indent: String, _ leftIndent: String, _ rightIndent: String) {
        left?.draw(leftIndent, leftIndent + "    ", leftIndent + " |  ")
        print(indent + " +- " + "\(value)")
        right?.draw(rightIndent, rightIndent + " |  ", rightIndent + "    ")
    }
}

extension Node: CollectionTypeConvertible {
    var array: [T] {
        return (left?.array ?? []) + [value] + (right?.array ?? [])
    }
}

print("# Int")
let tree = Node(value: 5)
tree.add(1)
tree.add(2)
tree.add(20)
tree.add(17)
print(tree)
tree.draw()

print("# String")
let strTree = Node(value: "hello")
strTree.add("yellow")
strTree.add("allow")
strTree.add("Allow")
strTree.add("Below")
print(strTree)
strTree.draw()

print("# Convert to Array")
let array = tree.array
print(array)
print(array.sort(>))
let strArray = strTree.array
print(strArray)
print(strArray.sort(>))