!!!DS and why? Thy are essential ingredients in creating fast and powerful algorithms. They help to manage and organize data. They make code cleaner and easier to understand. ADT (list, queue, map, vehicle) Complexity Analysis how much time does this algorithm need to finish? how much space does this algorithm need for its computation?……

vim十种寄存器 双引号代表的匿名寄存器，默认寄存器： "" 10个数字寄存器 “0 to 9 小删除寄存器 “-” 字母寄存器 “a to z or A to Z 只读寄存器冒号点号百分号 “:, “., “% 与buffer交……

GitHub Actions 有一些自己的术语。 （1）workflow （工作流程）：持续集成一次运行的过程，就是一个 workflow。 （2）job （任务）：一个 workflow 由一个或多个 jobs 构成，含义……

refector Extract Method Move Method Replace Conditional with Polyorphism Self Encapsulate Field Replace type code with State/Strategy……

Oracle查看树形数据路径: 1 2 3 4 5 select CONNECT_BY_ROOT title, --(根数据), -- (路径) sys_connect_by_path(title, '-->' ),level, --(层次) start with condition connect by parent_id = prior id……

Oracle 恢复数据如下： 1 2 -- 15分钟之前 select * from tablename as of timestamp sysdate-15/1440……

Oralce 空值排在前，或排在后边： 1 2 3 4 5 -- oracle 空值排序,排在最前面或者最后面 -- 1: order by name nulls first; -- 2: order by name nulls last;……

Oracle 按照特定值排序： 1 order by decode(field, num1, num2, num...)……

Oracle提供了merge into语法，如果数据不存在 就创建，如果数据已经存在就更新数据。用法如下： 1 2 3 4 5 6 7 8 9 10 11 12 13 MERGE INTO tablea A USING tableb B ON ( A.id = B.id ) WHEN MATCHED THEN……

2.（同时解决emacs使用卡顿现象） 1 2 3 4 5 6 7 8 9 10 11 12 13 14 ;; 更改显示字体大小 16pt ;; http://stackoverflow.com/questions/294664/how-to-set-the-font-size-in-emacs (set-face-attribute 'default nil :family "Fira Code Retina") (set-frame-font "Fira Code Retina:pixelsize=20") ;;中文字体的设置，同时解决中英文字体宽度不一致……