剑指offer——从上至下打印二叉树

 1 import java.util.ArrayList;
 2 /**
 3 public class TreeNode {
 4     int val = 0;
 5     TreeNode left = null;
 6     TreeNode right = null;
 7 
 8     public TreeNode(int val) {
 9         this.val = val;
10 
11     }
12 
13 }
14 */
15 public class Solution {
16     public ArrayList<Integer> PrintFromTopToBottom(TreeNode root) {
17         
18         ArrayList<Integer> list = new ArrayList<>();
19         ArrayList<TreeNode> queue = new ArrayList<>();
20         if(root==null)
21             return list;
22         queue.add(root);
23         
24         while(!queue.isEmpty())
25         {
26             TreeNode node= queue.remove(0);
27             
28             if(node.left!=null)
29                 queue.add(node.left);
30             if(node.right!=null)
31                 queue.add(node.right);
32             list.add(node.val);
33         }
34         return list;
35         
36     }
37 }