层序遍历二叉树的两种方法

public class test
{
	public static void main(String[] args) 
	{
		TreeNode root = new TreeNode(1);
		TreeNode r1 = new TreeNode(2);
		TreeNode r2 = new TreeNode(3);
		root.left = r1;
		root.right = r2;
		test.levelTraversal2(root);
	}
	//不使用队列
	public static void levelTraversal(TreeNode root)
	{
		ArrayList<TreeNode> list = new ArrayList<>();
		list.add(root);
		while(!list.isEmpty())
		{
			ArrayList<TreeNode> temp = new ArrayList<>();
			for (TreeNode node : list) 
			{
				System.out.print(node.val);
				if(node.left != null)
				{
					temp.add(node.left);
				}
				if(node.right != null)
				{
					temp.add(node.right);
				}
			}
			list = temp;
		}
	}
	
	//使用队列
	public static void levelTraversal2(TreeNode root)
	{
		ArrayDeque<TreeNode> queue = new ArrayDeque<>();
		queue.add(root);
		while(!queue.isEmpty())
		{
			TreeNode temp = queue.poll();
			System.out.print(temp.val);
			if(temp.left != null)
			{
				queue.offer(temp.left);
			}
			if(temp.right != null)
			{
				queue.offer(temp.right);
			}
		}
	}
}