题解 | #从上往下打印二叉树#

import java.util.*;
import java.util.ArrayList;
/**
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<>();
        Queue<TreeNode> q = new ArrayDeque<>();
        if(root == null) return result;
        q.add(root);
        while(!q.isEmpty()){
            TreeNode cur = q.poll();
            result.add(cur.val);
            if(cur.left != null) q.add(cur.left);
            if(cur.right != null) q.add(cur.right);
        }
        return result;
    }
}