从上往下打印二叉树

import java.util.ArrayList;
import java.util.LinkedList;
import java.util.Queue;


public class TreeNode {
    int val = 0;
    TreeNode left = null;
    TreeNode right = null;

    public TreeNode(int val) {
        this.val = val;

    }

}
*/
public class  {
    public ArrayList<Integer> PrintFromTopToBottom(TreeNode root) {
        Queue<TreeNode> queue = new LinkedList<>();
        ArrayList<Integer> result = new ArrayList<>();
        queue.add(root);
        while (!queue.isEmpty()) {
            int count = queue.size();
            while (count-- > 0) {
                TreeNode t = queue.poll();
                if (t == null){
                    continue;
                }
                result.add(t.val);
                queue.add(t.left);
                queue.add(t.right);
            }
        }
            return result;
    }
}