1 package com.algorithm;
2
3 import java.util.ArrayList;
4 import java.util.LinkedList;
5 import java.util.Queue;
6
7 //从上往下打印出二叉树的每个节点，同层节点从左至右打印。
8 /**
9 public class TreeNode {
10 int val = 0;
11 TreeNode left = null;
12 TreeNode right = null;
13
14 public TreeNode(int val) {
15 this.val = val;
16 }
17 }
18 */
19 public class PrintBinaryTree {
20 //思路 ，队列
21 public ArrayList<Integer> PrintFromTopToBottom(TreeNode root) {
22 ArrayList<Integer> ls = new ArrayList<Integer>();
23 if(root == null)
24 return ls;
25 Queue<TreeNode> queue = new LinkedList<TreeNode>();
26 queue.offer(root);//入队
27 while(!queue.isEmpty()){
28 TreeNode tn = queue.poll();//出对
29 ls.add(tn.val);//保存值
30 if(tn.left != null)
31 queue.offer(tn.left);//入队
32 if(tn.right != null)
33 queue.offer(tn.right);//出对
34 }
35 return ls;
36 }
37 }
