Java program to construct BST from given preorder traversal.

       
import java.io.*;
import java.util.*;

// Java program to construct BST from given preorder traversal

class Node {

    int data;
    Node left, right;

    Node(int d) {
        data = d;
        left = right = null;
    }
}

class BinaryTree {
   
    Node constructTree(int arr[], int start, int end) {
        Node root=null,head=null;
        if(end>0) {
            root=new Node(arr[start++]);
            head=root;
        } else return null;
        for(int i=start;i<=end;) {
            root=head;
            while(true) {
                if(root.data>=arr[i] && root.left!=null) {
                    root=root.left;
                } else if(root.data>=arr[i] && root.left==null){
                    root.left=new Node(arr[i++]);
                    break;
                }
                if(root.data<=arr[i] && root.right!=null) {
                    root=root.right;
                } else if(root.data<=arr[i] && root.right==null){
                    root.right=new Node(arr[i++]);
                    break;
                }
            }
        }
        return head;
    }
    
    void printInorder(Node node) {
        if (node == null) {
            return;
        }
        printInorder(node.left);
        System.out.print(node.data + " ");
        printInorder(node.right);
    }

    public static void main(String[] args) {
        BinaryTree tree = new BinaryTree();
        int pre[] = new int[]{10, 5, 1, 7, 40, 50};
        System.out.println("Inorder traversal of the constructed tree is ");
        Node root = tree.constructTree(pre,0,pre.length-1);
        tree.printInorder(root);
    }
}