题解 | #从上往下打印二叉树#

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

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

    }

}
*/
public class Solution {
    public ArrayList<Integer> PrintFromTopToBottom(TreeNode root) {
        Queue<TreeNode> q = new LinkedList<>();
        ArrayList<Integer> list = new ArrayList<>();
        if(root == null){
            return list;
       }
        q.offer(root);
        while(!q.isEmpty()){
            TreeNode node = q.poll();
            list.add(node.val);
            if(node.left != null){
                q.offer(node.left);
             }
            if(node.right != null){
                q.offer(node.right);
             }
        }
        return list;
    }
}