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

// The main method must be in a class named "Main".
// Method to calculate height of a tree
int height(Node root) {
    if (root == null)
        return 0;
    int leftHeight = height(root.left);
    int rightHeight = height(root.right);

    if (leftHeight > rightHeight)
        return leftHeight + 1;
    else
        return rightHeight + 1;
}

// Method to traverse the elements of a tree using BFS (level-order traversal) in recursive way
void levelOrderOrBFS() {
    int h = height(root);
    for (int i = 1; i <= h; i++)
        printNodesAtLevel(root, i, 1);
}

// Method to print nodes at the given level
void printNodesAtLevel (Node root, int level, int currentLevel) {
    if (root == null)
        return;
    if (level == currentLevel)
        System.out.print(root.data + " ");
    else {
        printNodesAtLevel(root.left, level, currentLevel + 1);
        printNodesAtLevel(root.right, level, currentLevel + 1);
    }
}