题解 | #从上往下打印二叉树#

import java.util.ArrayList;
import java.util.*;
/**
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) {
       ArrayList<Integer> result = new ArrayList<Integer>();
        if(root==null) return result;
        Queue<TreeNode> queue = new LinkedList<TreeNode>();
       queue.offer(root);
        while(!queue.isEmpty()){
            TreeNode temp = queue.poll();
            result.add(temp.val);
            if(temp.left!=null) queue.offer(temp.left);
            if(temp.right!=null) queue.offer(temp.right);
        }
        return result;
    }
}