BinaryTree.kt

import java.io.PrintStream

class Node(
    val value: Int,
    var left: Node? = null,
    var right: Node? = null


) {
    override fun toString(): String {
        return "Node(value=$value, left=$left, right=$right)"
    }
}

class BinaryTree {

    private var root: Node? = null

    fun add(value: Int) {
        root = recursive(root, value)
    }

    private fun recursive(current: Node?, value: Int): Node {
        if (current == null) {
            return Node(value)
        }
        if (value < current.value) {
            current.left = recursive(current.left, value)
        } else if (value > current.value) {
            current.right = recursive(current.right, value)
        } else {
            return current
        }
        return current
    }

    fun leafSum(): Int {
        return leftLeavesSum(root)
    }

    private fun isLeaf(node: Node?): Boolean {
        if (node == null)
            return false
        return node.left == null && node.right == null
    }

    private fun leftLeavesSum(node: Node?): Int {
        var res = 0

        if (node != null) {
            if (isLeaf(node.left))
                res += node.left!!.value
            else
                res += leftLeavesSum(node.left)

            res += leftLeavesSum(node.right)
        }

        return res
    }

    //print

    private fun traversePreOrder(sb: StringBuilder, padding: String?, pointer: String?, node: Node?) {
        if (node != null) {
            sb.append(padding)
            sb.append(pointer)
            sb.append(node.value)
            sb.append("\n")
            val paddingBuilder = StringBuilder(padding)
            paddingBuilder.append("│  ")
            val paddingForBoth = paddingBuilder.toString()
            val pointerForRight = "└──"
            val pointerForLeft = if (node.right != null) "├──" else "└──"
            traversePreOrder(sb, paddingForBoth, pointerForLeft, node.left)
            traversePreOrder(sb, paddingForBoth, pointerForRight, node.right)
        }
    }

    fun print(os: PrintStream) {
        val sb = StringBuilder()
        traversePreOrder(sb, "", "", this.root)
        os.print(sb.toString())
    }
}

fun main() {
    val bt = BinaryTree()

    bt.add(20)
    bt.add(9)
    bt.add(49)
    bt.add(23)
    bt.add(52)
    bt.add(15)
    bt.add(7)

    println(bt.print(System.out))
    println(bt.leafSum())
}