Checking if the tree is binary or not in swift.

isBST.swift

 class Node {
    var key : Int
    var left : Node?
    var right: Node?
    
    init(key: Int, left: Node?, right: Node?) {
        self.key = key
        self.left = left
        self.right = right
    }
 }
 
 func isBST(tree: Node) -> Bool {
    guard let left = tree.left, let right = tree.right else {
        return true
    }
    
    print ("current: \(tree.key)")
    print ("left: \(left.key) right: \(right.key)")
    if left.key <= tree.key && right.key > tree.key {
        if isBST(tree: left) && isBST(tree: right) {
            return true
        } else {
            return false
        }
    }
    
    return false
 }
 
 
 var secondLeftLeft = Node(key: 20, left: nil, right: nil)
 var seconLeftRight = Node(key: 35, left: nil, right: nil)
 var firstLeft = Node(key: 30, left:secondLeftLeft, right: seconLeftRight)
 
 
 var secondRightRight = Node(key: 51, left:nil, right: nil)
 var secondRightLeft = Node(key: 49, left:nil, right: nil)
 var firstRight = Node(key: 50, left:secondRightLeft, right: secondRightRight)
 
 var rootNode = Node(key: 40, left: firstLeft, right: firstRight )
 
 isBST(tree: rootNode)