Convert a Binary Tree to a Binary Search Tree using JavaScript

Last Updated : 01 Jul, 2024

Given a Binary Tree, the task is to convert it to a Binary Search Tree. The conversion must be done in such a way that it keeps the original structure of the Binary Tree.

Example: To demonstrate the conversion of the Binary Tree to the Binary Search Tree.

Approach

In this approach we are using Inorder Traversal and Sorting. To convert a binary tree to a BST, define a Node class and implement helper functions: newNode for node creation, printInorder for traversal, storeInorder to store inorder traversal in an array, and arrayToBST to update the tree with sorted values. In binaryTreeToBST , count the nodes, store and sort the inorder traversal, and update the tree. Finally, create a sample tree, convert it, and print its inorder traversal.

Example: The example below illustrates the Conversion of a binary tree to a binary search tree using JavaScript.

JavaScript

class Node {
    constructor(data) {
        this.left = null;
        this.right = null;
        this.data = data;
    }
}

let index = 0;
function newNode(data) {
    let temp = new Node(data);
    return temp;
}

function printInorder(node) {
    if (node == null)
        return;


    printInorder(node.left);

    console.log(node.data + " ");

    printInorder(node.right);
}

function arrayToBST(arr, root) {
    // Base Case
    if (root == null)
        return;

    arrayToBST(arr, root.left);
    root.data = arr[index];
    index++;
    arrayToBST(arr, root.right);
}


function storeInorder(node, inorder) {
    // Base Case
    if (node == null)
        return inorder;

    storeInorder(node.left, inorder);

    inorder[index] = node.data;
    index++;

    storeInorder(node.right, inorder);
}

function countNodes(root) {
    if (root == null)
        return 0;
    return countNodes(root.left) + countNodes(root.right) + 1;
}

function binaryTreeToBST(root) {

    if (root == null)
        return;

    let n = countNodes(root);
    let arr = new Array(n);
    arr.fill(0);

    storeInorder(root, arr);


    arr.sort(function (a, b) { return a - b });
    index = 0;
    arrayToBST(arr, root);
}

let root = null;

root = newNode(10);
root.left = newNode(30);
root.right = newNode(15);
root.left.left = newNode(20);
root.right.right = newNode(5);
binaryTreeToBST(root);

console.log("Following is Inorder Traversal of the converted BST: ");
printInorder(root);

Output

Following is Inorder Traversal of the converted BST: 
5 
10 
15 
20 
30

Time Complexity: O(n*logn)

Auxiliary Space: O(n)

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Convert a Binary Tree to a Binary Search Tree using JavaScript

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