题目描述
![在这里插入图片描述](https://img-blog.csdnimg.cn/cfb6732471554e179ab296d88e6e3f01.png?x-oss-process=image/watermark,type_ZHJvaWRzYW5zZmFsbGJhY2s,shadow_50,text_Q1NETiBA6ZSl5qCX,size_20,color_FFFFFF,t_70,g_se,x_16)
题解
很简单,分层的层序遍历,并且插入List<List<\Integer>>的时候按照倒叙插入即可(循环插入到list的头部)。
执行用时:1 ms, 在所有 Java 提交中击败了95.71%的用户
内存消耗:38.8 MB, 在所有 Java 提交中击败了16.68%的用户
通过测试用例:34 / 34
/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode() {}
* TreeNode(int val) { this.val = val; }
* TreeNode(int val, TreeNode left, TreeNode right) {
* this.val = val;
* this.left = left;
* this.right = right;
* }
* }
*/
class Solution {
List<List<Integer>> res = new ArrayList<>();
public List<List<Integer>> levelOrderBottom(TreeNode root) {
if (root == null)
return res;
Queue<TreeNode> q = new LinkedList<>();
q.offer(root);
while (!q.isEmpty()) {
int size = q.size();
List<Integer> temp = new ArrayList<>();
while (size > 0) {
TreeNode node = q.poll();
temp.add(node.val);
if (node.left != null) {
q.offer(node.left);
}
if (node.right != null) {
q.offer(node.right);
}
size--;
}
res.add(0, temp);
}
return res;
}
}