222. Count Complete Tree Nodes

    func countNodes(_ root: TreeNode?) -> Int {
        guard let root = root else { return 0}

        let leftH = heightLeft(root.left)
        let rightH = heightRight(root.right)

        if leftH == rightH {
            if leftH == 0 { return 1}
            return Int(pow(2.0, Double(leftH + 1))) - 1
        }
        return countNodes(root.left) + countNodes(root.right) + 1
    }

    func heightLeft(_ root: TreeNode?) -> Int{
        guard let root = root else {return 0}
        var h = 1
        var runner = root
        while runner.left != nil{
            runner = runner.left!
            h += 1
        }
        return h
    }
    func heightRight(_ root: TreeNode?) -> Int{
        guard let root = root else {return 0}
        var h = 1
        var runner = root
        while runner.right != nil{
            runner = runner.right!
            h += 1
        }
        return h
    }