# QA Official

### Knowledge Point 8: Common Sorting Algorithms-Select Sorting

https://qaofficial.com/post/2019/04/10/69784-knowledge-point-8-common-sorting-algorithms-select-sorting.html 2019-04-10
Yesterday we have introduced the principle and implementation of fast sorting, and we have also supplemented the execution process of selective sorting through several cyclic and progressive assumptions.However, it is a pity that these blogs have not been written on my computer. They use the new linux system and have no java execution environment or Android development environment.So blogs about Android series will be updated at the weekend.All right, let's not say much, let's continue our selection sorting algorithm.

### Matrix Connotation!It is helpful for the physical meaning of inverse matrix!

If you are not familiar with the concept of linear algebra and want to study natural science, it now looks like illiteracy.However, "according to the current international standards, linear algebra is expressed through axiomatization. it is the second generation of mathematical models, which brings difficulties in teaching."* What exactly is a matrix?Vectors can be considered as representations of objects with n mutually independent properties (dimensions). What is a matrix?If we think that a matrix is an expansion of a new composite vector composed of a set of column (row) vectors, then why is this expansion so widely used?

### Meng Yan BLOG Understanding Matrix One, Two, Three

https://qaofficial.com/post/2019/04/10/69845-meng-yan-blog-understanding-matrix-one-two-three.html 2019-04-10
Not long ago chensh wanted to act as a teacher and teach others linear algebra for ulterior purposes.Therefore, I was seized and discussed with him several times on some issues of falsity in linear algebra.Obviously, chensh felt that it was still relatively difficult for him not to be considered insane by that strong student when he was speaking linear algebra. Poor chensh, who let you go to this minefield?!Color makes one faint!

### Selection Sorting of Nine Sorting Algorithms (Principle and Implementation)

https://qaofficial.com/post/2019/04/10/69756-selection-sorting-of-nine-sorting-algorithms-principle-and-implementation.html 2019-04-10
1. Algorithm idea: Select sorting, scan the sequence from beginning to end, find the smallest element, exchange with the first element, and then continue this selection and exchange method from the remaining elements to finally obtain an ordered sequence. 2, algorithm process Take a chestnut (the sorting process of the first trip) Original sequence: 49, 38, 65, 97, 76, 13, 27, 49 1) In the process of selecting and sorting,

### Several Ways to Realize Thread Synchronization

Why use synchronization? java allows multi-thread concurrent control. When multiple threads simultaneously operate a shareable resource variable (e.g. data addition, deletion, modification and check),This will lead to inaccurate data and conflicts between them. Therefore, a synchronization lock is added to avoid being called by other threads before the thread completes its operation.Therefore, the uniqueness and accuracy of the variable are guaranteed. synchronization method 1. Synchronization MethodThat is, there is a

### Technical Requirements for Crossing Firewall

https://qaofficial.com/post/2019/04/10/69902-technical-requirements-for-crossing-firewall.html 2019-04-10
1. Problem Description The existence of network address translation and Firewall (NAT/FW) blocks various multimedia communication protocols including H.323, because NAT equipment only completes the translation of the address/port of the IP header of the message, making the information of the IP header of the message and the address/port in the message Payload inconsistent, resulting in that the message receiver cannot respond to the message correctly and the media flow channels of the communication parties cannot be established normally.

### Three common new Firewall technologies have their own advantages and disadvantages

From: http://cso.ccw.com.cn/news/htm2009/20090711 _ 1247309843644.shtml There are mainly three types of common Firewall: packet filtering, circuit layer gateway and Application Layer Gateway Service, each of which has its own advantages and disadvantages. Packet filtering is the first generation of Firewall technology. It checks all incoming packets according to security rules, which are mostly based on underlying protocols, such as IP and TCP.If a packet satisfies all the above rules, the filter router submits the data to the upper layer or forwards the packet, otherwise it discards the packet.

### Understand HTTPS process and principle

https://qaofficial.com/post/2019/04/10/69838-understand-https-process-and-principle.html 2019-04-10
Recently I want to rebuild my personal website+Upgrade to http/2 and learn some new knowledge.If you want to upgrade to http/2, you must upgrade your website to HTTPS first, because at this stage all browsers only support HTTP/2 Over TLS, that is, http/2 in browsers must be deployed based on https. What is https Because the general http protocol is transmitted in clear text and cannot be kept confidential, it is very unsafe to use http protocol to transmit secret information.

### Understand Matrix One:

https://qaofficial.com/post/2019/04/10/69881-understand-matrix-one.html 2019-04-10
Reprinted from: http://blog.csdn.net/myan/article/details/647511 Not long ago chensh wanted to act as a teacher and teach others linear algebra for ulterior purposes.Therefore, I was seized and discussed with him several times on some issues of falsity in linear algebra.Obviously, chensh felt that it was still relatively difficult for him not to be considered insane by that strong student when he was speaking linear algebra. Poor chensh, who let you go to this minefield?

### Understanding Matrix

https://qaofficial.com/post/2019/04/10/69848-understanding-matrix.html 2019-04-10
This is a summary of the "Understanding Matrix" article. The article explains the matrix from a different angle, which is quite interesting. Therefore, it is mainly to delete the original text and add one's own understanding. Importance of Linear Algebra: In his famous book Encounter with Mathematics, Swedish mathematician Lars Garding said: "If you are not familiar with the concept of linear algebra, you have to study natural science, and now it looks like illiteracy.