InvertBinaryTree.java

import java.util.*;

class TreeNode {
    int val;
    TreeNode left;
    TreeNode right;

    TreeNode(int val) {
        this.val = val;
        this.right=this.left=null;
    }
}
public static List<List<Integer>> zigzagLevelOrder(TreeNode root) {
    List<List<Integer>> result = new ArrayList<>();
    if (root == null) {
        return result;
    }

    Queue<TreeNode> queue = new LinkedList<>();
    queue.offer(root);
    boolean leftToRight = true;

    while (!queue.isEmpty()) {
        int size = queue.size();
        List<Integer> level = new ArrayList<>();

        for (int i = 0; i < size; i++) {
            TreeNode current = queue.poll();

            if (leftToRight) {
                level.add(current.val);
            } else {
                level.add(0, current.val);
            }

            if (current.left != null) {
                queue.offer(current.left);
            }
            if (current.right != null) {
                queue.offer(current.right);
            }
        }

        result.add(level);
        leftToRight = !leftToRight;
    }

    return result;
}
public class InvertBinaryTree {

    public static TreeNode buildTree(String[] nodes) {
        if (nodes == null || nodes.length == 0) {
            return null;
        }

        TreeNode root = new TreeNode(Integer.parseInt(nodes[0]));
        Queue<TreeNode> queue = new LinkedList<>();
        queue.add(root);

        int i = 1;
        while (!queue.isEmpty() && i < nodes.length) {
            TreeNode current = queue.poll();

            if (!nodes[i].equals("N")) {
                current.left = new TreeNode(Integer.parseInt(nodes[i]));
                queue.add(current.left);
            }
            i++;

            if (i < nodes.length && !nodes[i].equals("N")) {
                current.right = new TreeNode(Integer.parseInt(nodes[i]));
                queue.add(current.right);
            }
            i++;
        }

        return root;
    }

    public static TreeNode invertTree(TreeNode root) {
        if (root == null) {
            return null;
        }
 

        TreeNode temp = root.left;
        root.left = root.right;
        root.right = temp;

        invertTree(root.left);
        invertTree(root.right);

        return root;
    }

    public static void inorderTraversal(TreeNode root) {
        if (root != null) {
            inorderTraversal(root.left);
            System.out.print(root.val + " ");
            inorderTraversal(root.right);
        } 
    }
    public static void displayTree(TreeNode root) {
        if (root == null) {
            return;
        }

        Queue<TreeNode> queue = new LinkedList<>();
        queue.add(root);

        while (!queue.isEmpty()) {
            int size = queue.size();

            for (int i = 0; i < size; i++) {
                TreeNode current = queue.poll();
                System.out.print(current.val + "   ");

                if (current.left != null) {
                    queue.add(current.left);
                }

                if (current.right != null) {
                    queue.add(current.right);
                }
            }

            System.out.println();
        }
    }
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        String input = scanner.nextLine();
        scanner.close();
        String[] nodes = input.split(" ");
        TreeNode root = buildTree(nodes);
        root = invertTree(root);
        displayTree(root);
        inorderTraversal(root);
    }
}