level- order traversal

BFS

from: http://leetcode.com/2010/09/printing-binary-tree-in-level-order.html

public void breathFirstTraversalIterative(TreeNode root) {
        Queue queue = new LinkedList();
        TreeNode flagNode = new TreeNode("");
        queue.add(root);
        queue.add(flagNode);
        while (!queue.isEmpty()) {
            TreeNode node = queue.poll();
            if (node != flagNode) {
                System.err.print(node.val + " ");
                if (node.left != null)
                    queue.add(node.left);
                if (node.right != null)
                    queue.add(node.right);
            } else if (!queue.isEmpty())
                queue.add(flagNode);
        }
    }