hello-algo/en/codes/kotlin/chapter_tree/binary_search_tree.kt

/**
 * File: binary_search_tree.kt
 * Created Time: 2024-01-25
 * Author: curtishd (1023632660@qq.com)
 */

package chapter_tree

import utils.TreeNode
import utils.printTree

/* Binary search tree */
class BinarySearchTree {
    // Initialize empty tree
    private var root: TreeNode? = null

    /* Get binary tree root node */
    fun getRoot(): TreeNode? {
        return root
    }

    /* Search node */
    fun search(num: Int): TreeNode? {
        var cur = root
        // Loop search, exit after passing leaf node
        while (cur != null) {
            // Target node is in cur's right subtree
            cur = if (cur._val < num)
                cur.right
            // Target node is in cur's left subtree
            else if (cur._val > num)
                cur.left
            // Found target node, exit loop
            else
                break
        }
        // Return target node
        return cur
    }

    /* Insert node */
    fun insert(num: Int) {
        // If tree is empty, initialize root node
        if (root == null) {
            root = TreeNode(num)
            return
        }
        var cur = root
        var pre: TreeNode? = null
        // Loop search, exit after passing leaf node
        while (cur != null) {
            // Found duplicate node, return directly
            if (cur._val == num)
                return
            pre = cur
            // Insertion position is in cur's right subtree
            cur = if (cur._val < num)
                cur.right
            // Insertion position is in cur's left subtree
            else
                cur.left
        }
        // Insert node
        val node = TreeNode(num)
        if (pre?._val!! < num)
            pre.right = node
        else
            pre.left = node
    }

    /* Remove node */
    fun remove(num: Int) {
        // If tree is empty, return directly
        if (root == null)
            return
        var cur = root
        var pre: TreeNode? = null
        // Loop search, exit after passing leaf node
        while (cur != null) {
            // Found node to delete, exit loop
            if (cur._val == num)
                break
            pre = cur
            // Node to delete is in cur's right subtree
            cur = if (cur._val < num)
                cur.right
            // Node to delete is in cur's left subtree
            else
                cur.left
        }
        // If no node to delete, return directly
        if (cur == null)
            return
        // Number of child nodes = 0 or 1
        if (cur.left == null || cur.right == null) {
            // When number of child nodes = 0 / 1, child = null / that child node
            val child = if (cur.left != null)
                cur.left
            else
                cur.right
            // Delete node cur
            if (cur != root) {
                if (pre!!.left == cur)
                    pre.left = child
                else
                    pre.right = child
            } else {
                // If deleted node is root node, reassign root node
                root = child
            }
            // Number of child nodes = 2
        } else {
            // Get next node of cur in inorder traversal
            var tmp = cur.right
            while (tmp!!.left != null) {
                tmp = tmp.left
            }
            // Recursively delete node tmp
            remove(tmp._val)
            // Replace cur with tmp
            cur._val = tmp._val
        }
    }
}

/* Driver Code */
fun main() {
    /* Initialize binary search tree */
    val bst = BinarySearchTree()
    // Please note that different insertion orders will generate different binary trees, this sequence can generate a perfect binary tree
    val nums = intArrayOf(8, 4, 12, 2, 6, 10, 14, 1, 3, 5, 7, 9, 11, 13, 15)
    for (num in nums) {
        bst.insert(num)
    }
    println("\nInitialized binary tree is\n")
    printTree(bst.getRoot())

    /* Search node */
    val node = bst.search(7)
    println("Found node object is $node, node value = ${node?._val}")

    /* Insert node */
    bst.insert(16)
    println("\nAfter inserting node 16, binary tree is\n")
    printTree(bst.getRoot())

    /* Remove node */
    bst.remove(1)
    println("\nAfter removing node 1, binary tree is\n")
    printTree(bst.getRoot())
    bst.remove(2)
    println("\nAfter removing node 2, binary tree is\n")
    printTree(bst.getRoot())
    bst.remove(4)
    println("\nAfter removing node 4, binary tree is\n")
    printTree(bst.getRoot())
}