Are Trees Similar In Shape

I/P: 

24 10 20 50 -1 60 -1 -1 30 70 -1 80 110 -1 120 -1 -1 90 -1 -1 40 100 -1 -1 -1 24 1 2 5 -1 6 -1 -1 3 7 -1 8 11 -1 12 -1 -1 9 -1 -1 4 10 -1 -1 -1

O/P: true

1. first verify the size of children of both the nodes

2. if same, then tell their children to check their children further.

package pep.Day30;

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

public class Are_Trees_Similar_In_Shape {

    private static class Node {
        int data;
        ArrayList<Node> children = new ArrayList<>();
    }

    public static void display(Node node) {
        String str = node.data + " -> ";
        for (Node child : node.children) {
            str += child.data + ", ";
        }
        str += ".";
        System.out.println(str);

        for (Node child : node.children) {
            display(child);
        }
    }

    public static Node construct(int[] arr) {
        Node root = null;

        Stack<Node> st = new Stack<>();
        for (int i = 0; i < arr.length; i++) {
            if (arr[i] == -1) {
                st.pop();
            } else {
                Node t = new Node();
                t.data = arr[i];

                if (st.size() > 0) {
                    st.peek().children.add(t);
                } else {
                    root = t;
                }

                st.push(t);
            }
        }

        return root;
    }

    public static boolean areSimilar(Node n1, Node n2) {
        // write your code here
        if (n1.children.size() != n2.children.size())
            return false;
        else {
            for (int i = 0; i < n1.children.size(); i++) {
                boolean bool = areSimilar(n1.children.get(i), n2.children.get(i));
                if (!bool)
                    return false;
            }
        }

        return true;
    }

    public static void main(String[] args) throws Exception {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

        int n1 = Integer.parseInt(br.readLine());
        int[] arr1 = new int[n1];
        String[] values1 = br.readLine().split(" ");
        for (int i = 0; i < n1; i++) {
            arr1[i] = Integer.parseInt(values1[i]);
        }
        Node root1 = construct(arr1);

        int n2 = Integer.parseInt(br.readLine());
        int[] arr2 = new int[n2];
        String[] values2 = br.readLine().split(" ");
        for (int i = 0; i < n2; i++) {
            arr2[i] = Integer.parseInt(values2[i]);
        }
        Node root2 = construct(arr2);

        boolean similar = areSimilar(root1, root2);
        System.out.println(similar);
    }

}