标签：list node his pre highlight this 一个队列 deque lis
题目：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。
给定的树节点结构：
public class TreeNode {
int val = 0;
TreeNode left = null;
TreeNode right = null;
public TreeNode(int val) {
this.val = val;
}
}
二叉树的层次遍历，借助一个队列来实现。
代码如下：
public class Solution {
public ArrayList<Integer> PrintFromTopToBottom(TreeNode root) {
ArrayList<Integer> arrayList = new ArrayList<>();
Queue<TreeNode> queue = new ArrayDeque<>();
if (root != null) queue.offer(root);
while (!queue.isEmpty()) {
TreeNode node = queue.poll();
arrayList.add(node.val);
if (node.left != null) queue.offer(node.left);
if (node.right != null) queue.offer(node.right);
}
return arrayList;
}
}
标签：list node his pre highlight this 一个队列 deque lis
原文地址：https://www.cnblogs.com/yi-hui/p/8903865.html
