策略模式

class MallardDuck extends Duck {
    public MallardDuck() {
        quackBehavior = new Quack();
        flyBehavior = new FlyWithWings();
    }
}

class ModelDuck extends Duck {
    public ModelDuck() {
        quackBehavior = new Quack();
        flyBehavior = new FlyNoWay(); // 组合不同的方法
    }
}

class Main {
    public static void main(String[] args) {
        Duck real = new MallardDuck();
        Duck model = new ModelDuck();

        real.fly();
        model.fly(); // 调用同样的接口
    }
}

识别应用中变化的方面，把它们和不变的方面分开。

针对接口编程，而不是针对实现编程。

// Implement
Dog d = new Dog();
d.bark();

// Interface
Animal dog = new Dog();
dog.makeSound(); // abstract

优先使用组合而不是继承。

summary

策略模式定义了算法族并分别封装。策略让算法变化独立于使用它的客户。

DevTools

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-devtools</artifactId>
    <scope>runtime</scope>
    <optional>true</optional>
</dependency>

Spring CLI

可以用Spring Initializr或Spirng CLI来构建项目

spring init -list # 列出参数
# 初始化项目
spring init ( -d || --dependencies ) package1,package2 --build (maven/gradle) ( -p || --package) (war/jar) projectName
# Example
spring init -d web,jpa,security --build maven -p jar basic-project

spring init -d web,mustache,jpa,h2,devtools --package-name=com.example.blog --build maven mybloge

• Web: API服务
• JPA: 访问数据库的抽象
  项目结构图

$ tree basic-project/
basic-project/
├── HELP.md
├── mvnw # maven wrapper附带脚本
├── mvnw.cmd
├── pom.xml # maven 构建配置文件
└── src
    ├── main
    │   ├── java
    │   │   └── com
    │   │       └── example
    │   │           └── basic_project
    │   │               └── DemoApplication.java # 入口
    │   └── resources
    │       ├── application.properties # Configuration
    │       ├── static # 存放js/css,images
    │       └── templates # 存放页面模板
    └── test
        └── java
            └── com
                └── example
                    └── basic_project
                        └── DemoApplicationTests.java

15 directories, 7 files

Maven

换源

distributionUrl=https://maven.aliyun.com/repository/central/org/apache/maven/apache-maven/(edition.number)/apache-maven-(edition.number)-bin.zip

运行项目

mvn spring-boot:run
# 将会在localhost:8080运行

“When in doubt go to the library.” – J.K.Rowling

Catalog

Article1: What Are You Going to Do With That？

What Are You Going to Do With That？

William Deresiewicz（《国家》杂志撰稿人和《新共和》杂志编辑）在斯坦福大学的演讲

The question my title poses, of course, is the one that is classically aimed at humanities majors. What practical value could there possibly be in studying literature or art or philosophy? So you must be wondering why I’m bothering to raise it here, at Stanford, this renowned citadel of science and technology. What doubt can there be that the world will offer you many opportunities to use your degree?

（学习文学、艺术或哲学能有什么用呢？所以你肯定纳闷，我为什么在在以科技堡垒而闻名的斯坦福提出这个问题呢？在大学学位给人带来众多机会的问题上还有什么可怀疑的吗？）

But that’s not the question I’m asking. By “do” I don’t mean a job, and by “that” I don’t mean your major. We are more than our jobs, and education is more than a major. Education is more than college, more even than the totality of your formal schooling, from kindergarten through graduate school. By “What are you going to do,” I mean, what kind of life are you going to lead? And by “that,” I mean everything in your training, formal and informal, that has brought you to be sitting here today, and everything you’re going to be doing for the rest of the time that you’re in school.

（但那不是我提出的问题。这里的“做”并不是指工作，“那”并不是指你的专业。我们不仅仅是要个工作，教育不仅仅是学一门专业。教育也不仅仅是上大学，甚至也不仅是从幼儿园到研究生院的正规学校教育。我说的“你要做什么”的意思是你要过什么样的生活？我所说的“那”指的是你得到的正规或非正规的任何训练， 那些把你送到这里来的东西，你在学校的剩余时间里将要做的任何事。）

Hash

字母异位词

排序每一个单词，就知道是不是异位词。

两数之和

从数组中，找到nums[i] + nums[j] == target，并返回{ i, j }。
思路是双重循环，遍历每一个元素，求和是否为target。
然而，双重循环需要$O(N^2)$的复杂度。因此，可以使用一张表，使用containsKey方法识别是否存在当前i的target - nums[i]，即可减少一重循环。

关键思想

用Map高效率查找，减少一重循环。

最长连续序列

从乱序数组中，找到最长连续（数组中不一定连续）的序列。要求$O(N)$。
首先用数组的值存入哈希表，然后遍历数组，判断map.constains(curNum++)。
然而，即使这样还是效率不够高。

优化

1. 中间值不进入循环，序列开始值才进入，使用!contains(curNum - 1)判断是否为序列开始值
2. 去重，不要哈希表，不需要键值对，使用哈希Set，只存储值。

关键思想

去重；不处理中间值

一号标题

Title 2

三号标题

Title 4

五号标题

Title 6

• Unordered List
  • Unordered List

1. Ordered List
   2. Ordered List

• [x] TO-DO List
• [] TO-DO List

Delete Line
Blod
Italic
Code
$E = MC^2$
Link

^[1]Hello, World!

public static void main(String[] args) {
    System.out.println("Hello World!");
}

--- auto_detect: ture
+++ auto_detect: false

No Silver Bullet

By Brooks

[!NOTE]
Note that it is a note.

[!WARNING]
WARNING!

[!DANGER]
Notice the DANGER!

[!SUCCESS]
Now it is SUCCESS.

[!INFO]
Here is some INFO.

1.0 Bar 柱状图

from pyecharts.charts import Bar

bar = Bar()
bar.add_xaxis(["衬衣", "羊毛衫", "西装", "裤子", "鞋子", "袜子"])
bar.add_yaxis("商家", [5, 20, 40, 10, 70, 90])
# 相当于
bar = (
    Bar()
    .add_xaxis(["衬衣", "羊毛衫", "西装", "裤子", "鞋子", "袜子"])
    .add_yaxis("商家", [5, 20, 40, 10, 70, 90])
    .add_yaxis("商家B", [15, 6, 45, 20, 35, 66]) # 支持两个柱子同时生成
    .set_global_opts(title_opts=opts.TitleOpts(title="主标题", subtitle="副标题")) # 生成标题
)


bar.render("bar.html") # 渲染为 bar.html，默认是 render.html

• 效果

Author：aatalyk
Origin：Link

Before starting the topic let me introduce myself. I am a Mobile Developer currently working in Warsaw and spending my free time for interview preparations. I started to prepare for interviews two years ago. At that time I should say I could not solve the two sum problem. Easy problems seemed to me like hard ones so most of the time I had to look at editorials and discuss section. Currently, I have solved ~800 problems and time to time participate in contests. I usually solve 3 problems in a contest and sometimes 4 problems. Ok, lets come back to the topic.

Recently I have concentrated my attention on Dynamic Programming cause its one of the hardest topics in an interview prep. After solving ~140 problems in DP I have noticed that there are few patterns that can be found in different problems. So I did a research on that and find the following topics. I will not give complete ways how to solve problems but these patterns may be helpful in solving DP.

Patterns

1. Minimum (Maximum) Path to Reach a Target
2. Distinct Ways
3. Merging Intervals
4. DP on Strings
5. Decision Making

Tips

• 参考资料：https://note.tonycrane.cc/cs/system/pa/

1. 使用反向代理时，git相关命令会出问题
2. 实验前，创建新分支pa号，在其中做修改，完成以后合并pa到master中，并转回master分支

模板

# PA
## notification
- 
## difficulties
1. 
## summary

PA0

notification

• 全程使用git
• git commit --allow-empty可以使git空（无更改的）提交

笔记

命令

hexo new "postName" # 新建文章
hexo new page "pageName" # 新建页面
hexo generate # 生成静态页面至public目录
hexo server # 开启预览访问端口（默认端口4000，'ctrl + c'关闭server）
hexo deploy # 部署到GitHub
hexo help  # 查看帮助
hexo version  # 查看Hexo的版本

按文章更新时间排序

# Home page setting
# path: Root path for your blogs index page. (default = '')
# per_page: Posts displayed per page. (0 = disable pagination)
# order_by: Posts order. (Order by date descending by default)
index_generator:
  path: ''
  per_page: 10
  order_by: -updated # 默认是-date

背景设置

把你挑选的背景图片命名为：background.jpg，放在blog\themes\next\source\images里，在blog\themes\next\source\css_custom文件的custom.styl首部添加

body {
  background:url(/images/background.jpg);
  background-attachment: fixed;
}

符号链接

# Windows，有些文件需要文件名相同才能打开
# -d 目录符号链接
mklink /d C:\file\path\Target C:\file\path\Source

安装主题

1. npm安装在modules下

cd hexo-site
npm install hexo-theme-next

2. git clone安装

cd hexo-site
git clone https://github.com/next-theme/hexo-theme-next themes/next
# Upgrade
cd themes/next
git pull origin master
# Configuration
cp themes/next/_config.yml _config.next.yml

Hexo

我的配置

# 设置英文字体
global:
    family: Source Serif Pro

# layout\_partials\head\head.njk 设置中文字体
{{ next_font() }}
{{ next_vendors('fontawesome') }}
<link href="https://fonts.googleapis.com/css?family=Noto+Serif+SC&display=swap" rel="stylesheet">
# source\css\_variables\base.styl 添加中文字体
$font-family-chinese = "Noto Serif SC"

codes:
    family: IBM Plex Mono

codeblock:
  theme:
    light: stackoverflow-light

Quick Start

npm install hexo-cli -g
hexo init blogFolderName
cd blog
npm install
hexo server

Welcome to Hexo! This is your very first post. Check documentation for more info. If you get any problems when using Hexo, you can find the answer in troubleshooting or you can ask me on GitHub.

Create a new post

$ hexo new "My New Post"

More info: Writing

Run server

$ hexo server

More info: Server

Generate static files

$ hexo generate

More info: Generating

Deploy to remote sites

$ hexo deploy

More info: Deployment

使用

启动数据库

# 需要管理员权限
net start <mysql-service_name>

登录数据库

mysql -u <username> -p
$ <password>

导入数据库

-- 设置中文字符集
mysql> SET NAMES 'utf8mb4';
mysql> SET character_set_server = 'utf8mb4';
mysql> SOURCE /path/to/database.sql;

数据库

-- 创建数据库
CREATE DATABASE yourDatabase
  CHARACTER SET utf8mb4;

-- 查看所有数据库
show databases;

-- 进入数据库
use yourDatabase

表

-- 建表
CREATE TABLE yourTable (
  id   INT         AUTO_INCREMENT PRIMARY KEY,
  name varchar(50) NOT NULL       DEFAULT 'worker',
  age  INT         ,
  addr varchar(50) 
);

-- 删除表
drop <table>;

-- 查看表 
show tables;

-- 修改表
alter table <table>
add <col> char(20)
drop column <col>;

-- 删除整张表
drop table <table>;