import java.util.ArrayList;

import java.util.LinkedList;

import java.util.List;

import java.util.Queue;

class TreeNode

{

int val;

TreeNode left;

TreeNode right;

TreeNode(int val)

{

this.val = val;

left = null;

right = null;

}

}

public class BFSTree {

public List<Integer> BFStraversal(TreeNode tree)

{

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

List<Integer> list = new ArrayList<>();

if(tree == null)

{

return list;

}

queue.add(tree);

while(!queue.isEmpty())

{

TreeNode t = queue.poll();

list.add(t.val);

if(t.left != null)

{

queue.add(t.left);

}

if(t.right != null)

{

queue.add(t.right);

}

}

return list;

}

}

class BFSTreeDemo

{

public static void main(String[] args) {

BFSTree b = new BFSTree();

TreeNode tree = null;

tree = new TreeNode(10);

tree.left = new TreeNode(11);

tree.right = new TreeNode(15);

tree.left.left = new TreeNode(16);

tree.right.right = new TreeNode(17);

tree.left.right= new TreeNode(19);

tree.right.left = new TreeNode(20);

System.out.println(b.BFStraversal(tree));

}

}