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In computer science, an AVL tree (named after inventors Adelson-Velsky and Landis) is a self-balancing binary search tree. It was the first such data structure to be invented.[2] In an AVL tree, the heights of the two child subtrees of any node differ by at most one; if at any time they differ by more than one, rebalancing is done to restore this property. Lookup, insertion, and deletion all take O(log n) time in both the average and worst cases, where $n$ is the number of nodes in the tree prior to the operation. Insertions and deletions may require the tree to be rebalanced by one or more tree rotations.

Wikipedia

RAR被加密了不要扔，裹上鸡蛋液面包糠…

$$4.182$$

$$4.1820000000000003836930773104541003704071044921875$$

OK，说完背景，让我们再回到OJ的问题上来。

Spring Boot makes it easy to create Spring-powered, production-grade applications and services with absolute minimum fuss. It takes an opinionated view of the Spring platform so that new and existing users can quickly get to the bits they need.

Spring Boot通过其框架中的大量的自动化配置简化了原Spring项目中繁杂的配置步骤，可以轻松快速地搭建起Web服务，使得开发可以更加专注于业务逻辑。

# 起因

GCC-3.4就如同Linux 0.11一样，都是非常老的上古版本，软件源里早就不存在这么一号编译器了，于是我尝试了如下方案：

• 修改Makefile，去除版本限制——显然，编译失败
• 尝试从源安装GCC-3.4——但是源（ubuntu bionic@TUNA）根本就没有GCC-3.4
• 去Ubuntu官方的Old-Release手动拉取deb包安装，然后建立软链接，修改变量优先级——工具链的相互依赖关系难以解决，一不留神就会把系统默认的编译环境搞乱了。当然，还是以失败告终，并且这些上古工具安装到系统的不知道什么地方后，我怕会留下什么意料之外的后遗症，于是cp了个人文件后，去控制台把服务器重置了