剑指offer_二叉树---从上往下打印二叉树

/**
 * 
 */
package offerTest;
import java.util.ArrayList;
import java.util.LinkedList;
/**
 * <p>
 * Title:PrintFromTopToBottom
 * </p>
 * <p>
 * Description:
 * </p>
 * 
 * @author 田茂林
 * @data 2017年8月20日 下午9:15:55
 */
public class PrintFromTopToBottom {
    public ArrayList<Integer> ListPrintFromTopToBottom(TreeNode root) {
        ArrayList<Integer> list = new ArrayList<Integer>();
        LinkedList<TreeNode> queue = new LinkedList<TreeNode>();
        if (root == null) {
            return list;
        }
        queue.offer(root);
        while (!queue.isEmpty()) {
            TreeNode current = queue.poll();
            list.add(current.val);
            if (current.left != null) {
                queue.offer(current.left);
            }
            if (current.right != null) {
                queue.offer(current.right);
            }
        }
        return list;
    }
    public static void main(String[] args) {
        // TODO Auto-generated method stub
    }
}