Normal_BST_to_Balanced_BST.java

// { Driver Code Starts
import java.util.Scanner;
import java.util.*;
import java.lang.*;
import java.io.*;

class Node {
  int data;
  Node right, left;

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

class BinarySearchTree {
  static Node insert(Node node, int data) {
    if (node == null) {
      return (new Node(data));
    } else {

      /* 2. Otherwise, recur down the tree */
      if (data <= node.data) {
        node.left = insert(node.left, data);
      } else {
        node.right = insert(node.right, data);
      }

      /* return the (unchanged) node pointer */
      return node;
    }

  }

  int height(Node node) {
    if (node == null)
      return 0;
    else {
      int lDepth = height(node.left);
      int rDepth = height(node.right);
      if (lDepth > rDepth)
        return (lDepth + 1);
      else
        return (rDepth + 1);
    }
  }

  static Node buildTree(String str) {
    if (str.length() == 0 || str.charAt(0) == 'N') {
      return null;
    }

    String ip[] = str.split(" ");
    // Create the root of the tree
    Node root = new Node(Integer.parseInt(ip[0]));
    // Push the root to the queue

    Queue<Node> queue = new LinkedList<>();

    queue.add(root);
    // Starting from the second element

    int i = 1;
    while (queue.size() > 0 && i < ip.length) {

      // Get and remove the front of the queue
      Node currNode = queue.peek();
      queue.remove();

      // Get the current node's value from the string
      String currVal = ip[i];

      // If the left child is not null
      if (!currVal.equals("N")) {

        // Create the left child for the current node
        currNode.left = new Node(Integer.parseInt(currVal));
        // Push it to the queue
        queue.add(currNode.left);
      }

      // For the right child
      i++;
      if (i >= ip.length)
        break;

      currVal = ip[i];

      // If the right child is not null
      if (!currVal.equals("N")) {

        // Create the right child for the current node
        currNode.right = new Node(Integer.parseInt(currVal));

        // Push it to the queue
        queue.add(currNode.right);
      }
      i++;
    }

    return root;
  }

  public static void main(String[] args) throws IOException {

    BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

    int t = Integer.parseInt(br.readLine());

    while (t > 0) {
      String s = br.readLine();
      Node root = buildTree(s);

      GfG gfg = new GfG();

      root = gfg.buildBalancedTree(root);
      // preOrder(root);
      BinarySearchTree bst = new BinarySearchTree();
      System.out.println(bst.height(root));
      t--;
    }
  }

  void preOrder(Node node) {
    if (node == null)
      return;
    System.out.print(node.data + " ");
    preOrder(node.left);
    preOrder(node.right);
  }
}

class GfG {
  Node buildBalancedTree(Node root) {
    ArrayList<Integer> inorder = new ArrayList<>();
    inOrder(root, inorder);
    return balanceTree(inorder, 0, inorder.size() - 1);
  }

  Node balanceTree(ArrayList<Integer> inorder, int left, int right) {
    if (left > right)
      return null;
    int mid = left + (right - left) / 2;
    Node root = new Node(inorder.get(mid));
    root.left = balanceTree(inorder, left, mid - 1);
    root.right = balanceTree(inorder, mid + 1, right);

    return root;
  }

  void inOrder(Node root, ArrayList<Integer> inorder) {
    if (root == null)
      return;
    inOrder(root.left, inorder);
    inorder.add(root.data);
    inOrder(root.right, inorder);
  }
}