class NaryTreeNode {
    var parent: NaryTreeNode?
    var title: String?
    var son: [NaryTreeNode]?
    var level: Int = 0 // 层
    var frame: CGRect?
}
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struct NaryTreeConfig {
    var lineSpace: CGFloat = 30
    var interspace: CGFloat = 30
    var nodeSize = CGSize(width: 60, height: 60)
}
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class NaryTree: UIView {

    var config = NaryTreeConfig() {
        didSet {
            setupNodeFrame(node: root)
        }

    }

    var root: NaryTreeNode? {
        didSet {
            setupNodeFrame(node: root)
        }
    }

    override func draw(_ rect: CGRect) {
        super.draw(rect)
        drawNode()
    }
}

private extension NaryTree {
    func drawNode() {
        guard let root = root else { return }
        var stack = [NaryTreeNode]()
        stack.append(root)
        drawCircle(frame: root.frame)
        while !stack.isEmpty {
            let node = stack.removeLast()
            guard let son = node.son else { return }
            for child in son {
                stack.insert(child, at: 0)
                drawCircle(frame: child.frame)
            }
        }
    }

    func drawCircle(frame: CGRect?) {
        guard let context = UIGraphicsGetCurrentContext(),
              let frame = frame
        else {
            return
        }
        UIColor.red.set()
        let path = UIBezierPath(arcCenter: CGPoint(x: frame.midX, y: frame.midY), radius: config.nodeSize.width / 2, startAngle: 0, endAngle: 360, clockwise: true).cgPath
        context.addPath(path)
        context.fillPath()
    }
}


private extension NaryTree {

    func setupNodes() {
        setupNodeFrame(node: root)
        setNeedsDisplay()
    }

    func setupNodeFrame(node: NaryTreeNode?) {
        var minX: CGFloat = -config.nodeSize.width - config.interspace
        guard let node = node else { return }
        levelOrder(node)
        calculateFrame(node: node, minX: &minX)
    }

    func calculateFrame(node: NaryTreeNode, minX: inout CGFloat) {
        guard let son = node.son,
              son.isEmpty == false
        else {
            minX += config.nodeSize.width + config.interspace
            let y = CGFloat(node.level) * config.lineSpace + CGFloat(node.level) * config.nodeSize.height
            node.frame = CGRect(x: minX, y: y, width: config.nodeSize.width, height: config.nodeSize.height)
            return
        }
        son.enumerated().forEach { _, child in
            calculateFrame(node: child, minX: &minX)
        }
        guard let minx = son.first?.frame?.origin.x,
              let maxX = son.last?.frame?.origin.x else { return }
        let x = (minx + maxX) / 2.0
        let y = CGFloat(node.level) * config.lineSpace + CGFloat(node.level) * config.nodeSize.height
        node.frame = CGRect(x: x, y: y, width: config.nodeSize.width, height: config.nodeSize.height)
    }
    /// 层序遍历
    func levelOrder(_ root: NaryTreeNode?) {
        guard let root = root else { return }
        var stack = [NaryTreeNode]()
        stack.append(root)
        while !stack.isEmpty {
            let node = stack.removeLast()
            guard let son = node.son else { return }
            for child in son {
                stack.insert(child, at: 0)
                child.level = node.level + 1
            }
        }
    }
}