投稿時間:2022-02-21 20:35:30 RSSフィード2022-02-21 20:00 分まとめ(35件)

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TECH	Engadget Japanese	従来の2/3の時間で窓拭きが完了。アプリやリモコンで遠隔制御可能な窓拭きロボット「iCina」	https://japanese.engadget.com/icina-robot-105021556.html	アプリやリモコンで遠隔制御も可能min㎡の速度水拭き・乾拭きのモードで効率よく清掃KPaの吸着力で窓に限らず滑らかな平面ならどこでも使用可能窓の掃除をする際、窓の外側が掃除しにくい、上の方まで届かない、窓が多くて掃除が大変・・・そんな窓掃除のお悩みを解決するのが窓拭きロボット「iCina」です。	2022-02-21 10:50:21
IT	ITmedia 総合記事一覧	[ITmedia ビジネスオンライン] 北京五輪のメダル獲得数ランキング　3位「ドイツ」、2位「ROC」、1位と日本の順位は？	https://www.itmedia.co.jp/business/articles/2202/21/news171.html	ITmediaビジネスオンライン北京五輪のメダル獲得数ランキング位「ドイツ」、位「ROC」、位と日本の順位は月日に北京五輪が閉幕し、各国のメダル獲得数が確定した。	2022-02-21 19:41:00
IT	ITmedia 総合記事一覧	[ITmedia Mobile] Kyash発行のVisaカードでさらにポイントがたまる「Kyashリワード」開始	https://www.itmedia.co.jp/mobile/articles/2202/21/news170.html	itmediamobilekyash	2022-02-21 19:20:00
python	Pythonタグが付けられた新着投稿 - Qiita	yukicoder No.485 方程式のお勉強	https://qiita.com/ryusuke920/items/5d4a5c4b903901483b07	yukicoderNo方程式のお勉強今回もyukicoderの問題紹介・解説を行っていきたいと思います問目に紹介する問題はこちら概要問題No方程式のお勉強レベル実行時間制限ms問題文へのリンク↓↓問題文九郎くんは、方程式を解くことにハマりはじめています。	2022-02-21 19:24:11
python	Pythonタグが付けられた新着投稿 - Qiita	yukicoder No.1012 荷物収集	https://qiita.com/ryusuke920/items/e507f175d1245a49f92e	各ileqileqQに対して、すべての荷物を位置Xiに運ぶための必要最低限の合計コストをそれぞれ求めて行ごとに出力してください。	2022-02-21 19:07:34
python	Pythonタグが付けられた新着投稿 - Qiita	特徴量の選択について勉強したことをまとめてみた	https://qiita.com/insilicomab/items/cf67ffe1232feaab8d37	その後、各特徴量を繰り返し評価し、損失や評価指標が改善された場合に「有望な特徴量」のリストに追加していく。	2022-02-21 19:02:21
js	JavaScriptタグが付けられた新着投稿 - Qiita	scriptタグの書き方【同期的読み込みと非同期的読み込み】	https://qiita.com/y-suzu/items/a3d55aa709d910f029f7	async属性と同じく非同期にJavaScriptファイルのダウンロードと実行をするため、DOM構築を停止しません。	2022-02-21 19:06:55
js	JavaScriptタグが付けられた新着投稿 - Qiita	Discord.js(v13系)で指定チャンネルにメッセージ送信メモ	https://qiita.com/n0bisuke/items/cc4deef076ecf86421f5	Discordjsv系で指定チャンネルにメッセージ送信メモ呼びかけてリプライさせるなどではなく、別のプログラムからWebhook使う形でも良いのですが、毎回WebhookURLを発行するのも手間になってきたので、調べてみました。	2022-02-21 19:04:30
Ruby	Rubyタグが付けられた新着投稿 - Qiita	RSpecの書き方２(before do)	https://qiita.com/sekkenn1102/items/1afad643371190fd7619	endendendbeforedoを用いることで上記のようにログイン処理をまとめることができます。	2022-02-21 19:15:01
AWS	AWSタグが付けられた新着投稿 - Qiita	AWS認定資格　無料WEB問題集解説(一部)	https://qiita.com/a_kenkyu/items/67f4f8e58a3d72fc208c	APNパートナーがAWSベースのビジネスやソリューションの構築に成功するよう支援することに重点を置いていますAWSコンサルティングパートナービジネス構築リソース、プログラム、マーケティングリソース、資金調達のためのリソースがコンサルティングパートナーの利点です。	2022-02-21 19:11:45
Ruby	Railsタグが付けられた新着投稿 - Qiita	Railsで1対1のモデル関連付けを学習する	https://qiita.com/Shuhei_Nakada/items/10934e52a9f7ee03cc10	Railsで対のモデル関連付けを学習するはじめにこれまで対の関連付けをしたことがなかったので実装して検証してみました。	2022-02-21 19:51:11
海外TECH	DEV Community	How to Secure your NodeJs Express Javascript Application - part 2	https://dev.to/smartscanner/how-to-secure-your-nodejs-express-javascript-application-part-2-1oah	How to Secure your NodeJs Express Javascript Application part Express is an easy to use web framework for NodeJs In this article we will review some of the common vulnerabilities in NodeJs Express projects and explain mitigations against them Let s see how we can make our Express software more secure Limit inputAllowing clients to send huge request body can be abused for a denial of service DoS attack To prevent DoS attacks always set a maximum request size for the input Use the below code to limit input size var contentType require content type var express require express var getRawBody require raw body var app express app use function req res next getRawBody req length req headers content length limit mb encoding contentType parse req parameters charset function err string if err return next err req text string next You can also set request size for different content types app use express urlencoded extended true limit kb app use express json limit kb Other than input size you should limit the Transaction per Second Minute TPS TPM rate If you don t set a rate limitation for your sensitive APIs like login you expose yourself to a Brute Force attack Packages like express brute express bouncer and express limiter are some sample packages you can use for limiting input rate in Express Below code is a sample code for protecting against brute force attacks const express require express const ExpressBrute require express brute const login require routes login js const app express using memory store an in memory db is recommended for productionlet store new ExpressBrute MemoryStore let bruteforce new ExpressBrute store app post auth bruteforce prevent login Note If you use an API gateway like Kong you can easily configure input limiting policies for your routes Note CAPTCHA and account lockout are also other common solutions for mitigating brute forcing attacks Bonus You can also benefit from packages like toobusy js for monitoring the load of your server to detect whether you re under a DoS attack Remove old forgotten debug and unused routesIt s common but not recommended to add debug routes during development for testing purposes These routes usually don t have authentication and they re less restricted The path to these routes is usually easy to guess something like test This allows attackers to find them easily and abuse the functionality Review all the routes in your Express project and remove any unnecessary routes and use proper testing and versioning scheme to prevent unwanted routes in production Bonus Another example of unwanted routes are default routes like those available in Sails and Feathers Fortunately Express only has a default error and handlers which we will cover in the following section Catch and errorsYou should always expect exceptions to happen so get prepared Unhandled exceptions throw a ton of information to users Default NodeJs exceptions disclose information like Operation System and used libraries Instead of displaying a detailed error message you can add an error handling middleware to catch all errors like below app use err req res next gt  console error err stack  res status send Something broke Note You should add the above middleware after any other app use and routes No need to mention that you can capture any exception in NodeJs by subscribing to uncaughtException event on the process object Write clean codeCode quality is directly correlated to software security Less code hides fewer vulnerabilities right So does the clean code Keeping your Express project as clean as possible helps to increase the security of your JavaScript application One example of bad code that is common in JavaScript projects is the Callback Hell Callback Hell also known as Pyramid of Doom is an anti pattern seen in code of asynchronous programming It happens when callbacks are nested inside each other It s easy to get lost in a callback hell because it s hard to follow the execution flow of the program Inside those deep nested callbacks security bugs unhandled exceptions and information leakage are waiting for the right moment to strike It s important to have a proper Secure SDLC process in place to prevent bad code Things like enabling security linters code reviews and automatic code scan like Github code scan see this repo are good controls for having more secure code Only return what is necessaryWhen passing information to the clients always return the minimum possible fields Consider a use case where you want to show a list of available users on your website You can query the database for all users and return a list of users with all their attributes and only display the username on the front end Properties like username password address social security numbers and many others are usually associated with users You might not display all of them on the page but you are exposing them in your API which makes them available for hackers Do not use evalThere are some functions you must avoid calling unless you absolutely have to use them eval is one of them The eval function evaluates JavaScript code represented as a string It is far too easy for a bad actor to run arbitrary code when you use eval with user supplied input The NodeJs child process exec is similar to eval and should be avoided The fs and vm modules as well as the RegExp class should be used carefully if you want to pass user input to them Please read the input validation on part of this series for more Use strict modeJavaScript s strict mode introduced in ECMAScript is a way to opt in to a restricted variant of JavaScript Strict mode makes several changes to normal JavaScript semantics It eliminates some JavaScript silent errors by changing them to throw errors It also helps JavaScript engines perform optimizations and prohibits some syntax likely to be defined in future versions of ECMAScript For all these improvements it s encouraged to always use strict mode For activating strict mode add strict mode at top of your code Log and monitor eventsRecord any events on your application and review them Monitoring logs regularly could help identify malicious activities on your system When something bad happens logs are your only way to find out what happened and what is the root cause of it In Express you can use express winston for logging	2022-02-21 10:51:03
海外TECH	DEV Community	Find minimum in rotated sorted array in Python(code and explanation)	https://dev.to/riyu/find-minimum-in-rotated-sorted-array-in-pythoncode-and-explanation-hm4	Find minimum in rotated sorted array in Python code and explanation Problem statementSuppose an array of length n sorted in ascending order is rotated between and n times For example the array nums might become if it was rotated times if it was rotated times Notice that rotating an array a a a a n time results in the array a n a a a a n Given the sorted rotated array nums of unique elements return the minimum element of this array You must write an algorithm that runs in O log n time Example Input nums Output Explanation The original array was rotated times IntuitionFrom the question we can easily understand that it is a Binary Search question Hints Sorted and expectedTime Complexity logn But we cannot directly apply it ImplementationSo if the array is rotated then we can say that now the entire array is divided into two different sorted arrays for eg from index to the array is sorted and from index to the array is sorted But from index to the array is not sorted Also we can say that if any number from array is greater than its first element than it is sorted Then we will look for our number in right part of array i el mid And if any number is less than its first element than it is not sorted from first index to mid Then we will look for our number in left part of array i eh mid Also in the array the smallest number will be the number that is smaller than both its previous and next elementHence we will check if nums mid lt nums mid return nums mid if nums mid lt nums mid return nums mid Codeclass Solution def findMin self nums List int gt int if len nums return nums l h len nums if nums h gt nums return nums while l lt h mid l h if nums mid lt nums mid return nums mid if nums mid lt nums mid return nums mid if nums mid gt nums l mid else h mid Time ComplexityO logn as we are using binary search itself with some changes Space ComplexityO No extra space required similar to binary search	2022-02-21 10:42:02
海外TECH	DEV Community	How I Escaped Tutorial Hell	https://dev.to/jpoly1219/how-i-escaped-tutorial-hell-4g4p	How I Escaped Tutorial HellImage generated by Meme GeneratorLet me tell you something kid A long long time ago in a galaxy far far away a man like so many others before him left to the tutorial hell Legends say he never returned Don t be like him Developer about to watch his th tutorial on how to create a blog web appWhen Dante first wrote Inferno he describes his experience traveling left to the tutorial hell like so many others before him through the nine different circles of hell Being a th century man Dante probably didn t know of the existence of one hell the seemingly benign but the most sinister and enfeebling of them all tutorial hell Today we are blessed with an abundance of tutorials It is really easy to get started in almost anything that you want to do There are also lots of high quality tutors and teachers on YouTube Udemy etc With so much guidance you d expect nothing to go wrong right Everyone can achieve their dreams and no one will be left frustrated right Reality is never that rosy The cornucopia of tutorials and guides has fostered a new breed of developers those stuck in the infinite loop of tutorial hell I was no exception as well but I have managed to escape the vicious cycle In this post I d like to share my experiences and give advice to those yet to escape Image sourced from gfycat How I got trapped in the tutorial hellIt was back when I was in high school I just taught myself how to write simple code in Python It was good and all but I quickly realized that printing out Hello World on a console with a for loop isn t the most useful thing to do So I went on a soul searching journey that is I googled what I can do with Python I came up with the following list Data scienceAI MLWeb developmentI decided to go with web development because I wasn t interested in the first two topics at the time Also one of my teachers recommended to me this thing called Django So because my knowledge of Django and web development was akin to that of a three year old kid I thought that it was a good idea to watch tutorials put together by people who are well versed in the topic I watched a tutorial from Traversy Media and actually finished the entire series At this point I had a blog web app up and running and I felt pretty proud of myself Ok let s see if I can do this from scratch again I couldn t do it Nothing came to my mind and I was left dazed and confused A humiliating defeat Was the tutorial bad Probably not Which means that I m probably really bad I should watch more tutorials and learn Young Jacob about to step his first foot into tutorial hell The feedback loop getting stuck feels bad but trying to get out feels abysmalTutorials are powerful They are a good source of knowledge But it is a very protean and malleable substance It takes the form of whatever you want it to be This is an issue because for most people tutorials take the form of copium Image generated by Meme GeneratorThis might sound a bit harsh but I think many people use tutorials as a coping mechanism Watching these tutorials make us feel as if we know our stuff We feel confident and copying code verbatim following the steps through and seeing immediate results can be a major ego boost But as soon as we try to make something ourselves we get pummeled by the harsh reality We haven t actually learned anything I am not off the hook on this I watched hundreds of these How to make X tutorials and racked up thousands of hours of playtime Every time I watched these videos I felt awesome I felt like I was being productive and I was making something useful I have a folder on my laptop that holds all my code from tutorials and there are lots of dead blogging web apps and to do list apps One tutorial done great another web app to throw at the folder of oblivion I have to admit the state I was in was pretty pathetic Let s make it clear watching tutorials to learn is fine but being addicted to tutorials is lying to yourself and is a form of instant gratification that we need to cut How to end this cycleWatch the tutorial Then try to recreate the same thing without looking at the tutorial Fail Your ego thinks you can do it but your brain realizes that you actually can t Feel the cognitive dissonance Let that sink in a bit This is a good wake up call You need to realize that relying on the tutorial isn t going to help you in any way It s like doing homework The less you care the more likely you are to cheat and copy answers off Chegg or Sladers You need to care more Think of why you wanted to start programming in the first place Is it because you find the concept genuinely interesting Is it because you like building cool things Or is it just for the money Whatever the reason may be if you set your purposes clearly then you will be able to build intrinsic motivation In other words make yourself want to do programming because you genuinely want to achieve something great Also remember don t compare yourself to other developers so much It s like comparing apples to oranges Everyone is playing a different game and their rules slightly differ from yours Don t get crushed under the pressure to do better than everyone else It is your first attempt at creating something yourself and Rome wasn t built in a day Instead trust the process and keep up the honest work To me the ideal way to learn programming consists of the following steps Find something that you want to work on or create Brainstorm and design the app s structure What functionality will it have How is it going to be implemented Each functionality can be created into its respective module Split your project up into smaller more manageable bits Pick your weapon of choice Watch a tutorial or read the documentation to get a gist of how to use the tools you have picked Using those tools try making these modules yourself Only look up documentation and tutorials when you get stuck Repeat step until you are done I followed the above steps and I escaped the vicious cycle before I even realized it ConclusionTutorial hell is a trap that many new developers fall into and it is a tough one to escape However it is something you can overcome Know that many before you have succumbed to instant gratification as you have But also know that many of them actually managed to escape So don t lose hope discipline yourself and trust the process Thank you for reading I hope this post can help new developers get over the tutorial hell and become strong You can also view this post on Medium and my personal website Best of luck Jacob	2022-02-21 10:41:43
海外TECH	DEV Community	What is an EnumMap in Java?	https://dev.to/maddy/what-is-an-enummap-in-java-3pm6	What is an EnumMap in Java Some days ago I bumped into an error on Intellij I don t remember specifically what it was But I remember Intellij suggesting I use an enumMap I knew about the existence of enums but I wasn t aware of the existence of enumMaps So here is an article covering enumMaps in Java What is an EnumMap An EnumMap is a special form of a map A map in Java is an interface that takes a key K and a value V In the case of an EnumMap the key is an enum An EnumMap extends the AbstractMap implements Map interface How to create an EnumMapTo create an enumMap we have to import the java util EnumMappublic class JavaEnumMap enum Colour RED BLUE BLACK GREEN How to add an element into an enumMapYou can use the put method to insert elements into an enumMap public static void main String args EnumMap lt Colour Integer gt colours new EnumMap lt Colour Integer gt Colour class colours put Colour RED colours put Colour BLUE colours put Colour BLACK colours put Colour GREEN How to access an element on an enumMapTo access the elements of an enumMap you can use keySet It prints all the keys on the mapSystem out println Printing all keys in the map colours keySet The result is Printing all keys in the map RED BLUE BLACK GREEN entrySet It prints the keys and the values in the mapSystem out println Printing the keys and the values in the map colours entrySet The result is Printing the keys and the values in the map RED BLUE BLACK GREEN values It prints the values in the mapSystem out println Printing the values in the map colours values The result is Printing the values in the map How to retrieve elements from an enumMapYou can use the get method to retrieve elements from an enumMap System out println Retrieve the value from the enumMap colours get Colour RED The result is Retrieve the value from the enumMap How to remove elements from an enumMapTo remove elements from an enumMap you can use remove key You use the key of the enumMap to remove an element from an enumMapSystem out println Removing the key colours remove Colour GREEN The result is Removing the key The enumMap now has RED BLUE remove key value If it exists it removes the element from the enumMap and returns a boolean value System out println Removing the key and the value from the enumMap colours remove Colour BLACK Removing the key and the value from the enumMap trueThe enumMap now has RED BLUE The result is The enumMap now has RED BLUE How to replace an enumMapreplace key value It replaces the old value with a new value colours replace Colour RED System out println The new enum now has colours Result is The new enum now has RED BLUE replace key oldValue newValue This method replaces the old value with a new one only if the old value is linked with a specific key colours replace Colour BLUE System out println The new enum now has colours The result is The new enum now has RED BLUE replaceAll It replaces the value of each element with the result of the function colours replaceAll key oldValue gt oldValue System out println EnumMap using replaceAll colours The result is EnumMap using replaceAll RED BLUE A few notes about enumMaps EnumMaps maintain the natural order of their keys We cannot have null keys Internally enumMaps are represented as arrays CONCLUSIONIn this article you ve learned about enumMaps and its methods I hope you ve found this article helpful If you enjoy my writing please consider subscribing to my newsletter I m also on LinkedIn and Twitter Until next time ‍ ️ADDITIONAL RESOURCESJavaDoc EnumMapBaeldung A Guide to EnamMapRitesh Panigrahi Complete Guide to Java Enum	2022-02-21 10:19:01
海外TECH	DEV Community	introduction to CSS Framework(Bootstrap)	https://dev.to/sardiusjay/introduction-to-css-frameworkbootstrap-56n0	introduction to CSS Framework Bootstrap IntroductionThere are different aspect of making using of framework in web development and more essentially in the area of a frontend Engineer which entails the framework for CSS and JavaScript for the CSS framework we have the framework which are Tailwind and Bootstrap while for JavaScript framework we have Reactjs Vuejs and AngularJs but we are going to be discussing about Bootstrap Prerequisitebefore you start making use of this front end framework there is need for you to understand the fundamentals which can also be referred to as prerequisiteAnd this understand can only be the way forward to making use of the Bootstrap framework as a frontend developer this entails having understanding on how to use HTML And CSSBut there must be willingness to learn and understand this to be able to use Bootstrap very well The goal of this articleAfter reading this article to the end every reader should be able to Understand what Bootstrap is What it include and the functions it can perform The reason for making use of Bootstrap with Html and CSS What is BootstrapBootstrap is a free front end framework for faster and easier web development it include HTML and CSS based design templates for typography forms buttons tables navigation modals image carousels and many other as well as optional JavaScript pluginsThere are different type of BootstrapBootstrap Bootstrap Bootstrap There was upgrade in the development of this framework Bootstrap and from and now to and it has been able to work in different way I mean better than those available before so we are discussing Bootstrap which i will advice you to go Note The Bootstrap requires a containing element to wrap site contents Bootstrap Containerwhat is a container in Bootstrap Containers are used to pad the content inside of them and there are two container classes available The container class provides a responsive fixed width containerThe container fluid class provides a full width container spanning the entire width of the viewportAnd there different container Sections Fixed ContainerA sample of how the fixed container is programed lt div class container gt lt h gt My First Bootstrap Page lt h gt lt p gt This is some text lt p gt lt div gt Fluid ContainerA sample of how the fixed container is programed lt div class container fluid gt lt h gt My First Bootstrap Page lt h gt lt p gt This is some text lt p gt lt div gt Container PaddingA sample of how the fixed container is programed lt div class container pt gt lt div gt Container Border and ColorA sample of how the fixed container is programed lt div class container p my border gt lt div gt lt div class container p my bg dark text white gt lt div gt lt div class container p my bg primary text white gt lt div gt Responsive ContainersA sample of how the fixed container is programed lt div class container sm gt container sm lt div gt lt div class container md gt container md lt div gt lt div class container lg gt container lg lt div gt lt div class container xl gt container xl lt div gt What it include and the functions it can perform Bootstrap it makes the website responsive and which makes automatically adjust themselves to look good on all devices from small phones to large desktops it include a lot and functions that help you easily as a frontend engineer get your design done in less time than you think Functions it can performi have discuss one of the functions the bootstrap can perform to make it more responsive which is the Container and others will be listed below Follow and enjoy the ride Bootstrap CardA card in Bootstrap is a bordered box with some padding around its content It includes options for headers footers content colors etc Basic CardA basic card is created with the card class and content inside the card has a card body class lt div class card gt lt div class card body gt Basic card lt div gt lt div gt And in a Card we have the Header Content and the footer a code that display how it is arranged on a card lt div class card gt lt div class card header gt Header lt div gt lt div class card body gt Content lt div gt lt div class card footer gt Footer lt div gt lt div gt And to add a background color we are going to be making use of Contextual Cards lt DOCTYPE html gt lt html lang en gt lt head gt lt title gt Bootstrap Example lt title gt lt meta charset utf gt lt meta name viewport content width device width initial scale gt lt link rel stylesheet href dist css bootstrap min css gt lt script src dist jquery slim min js gt lt script gt lt script src dist umd popper min js gt lt script gt lt script src dist js bootstrap bundle min js gt lt script gt lt head gt lt body gt lt div class container gt lt h gt Cards with Contextual Classes lt h gt lt div class card gt lt div class card body gt Basic card lt div gt lt div gt lt br gt lt div class card bg primary text white gt lt div class card body gt Primary card lt div gt lt div gt lt br gt lt div class card bg success text white gt lt div class card body gt Success card lt div gt lt div gt lt br gt lt div class card bg info text white gt lt div class card body gt Info card lt div gt lt div gt lt br gt lt div class card bg warning text white gt lt div class card body gt Warning card lt div gt lt div gt lt br gt lt div class card bg danger text white gt lt div class card body gt Danger card lt div gt lt div gt lt br gt lt div class card bg secondary text white gt lt div class card body gt Secondary card lt div gt lt div gt lt br gt lt div class card bg dark text white gt lt div class card body gt Dark card lt div gt lt div gt lt br gt lt div class card bg light text dark gt lt div class card body gt Light card lt div gt lt div gt lt div gt lt body gt lt html gt The code above give illustrations of the different color that is imbedded in Bootstrap that can be use check and enjoy the moment The reason for making use of Bootstrap with Html and CSS The need for responsiveness in a Website or a Web page cannot be overemphasized and making a frontend engineer happy and making the work awesomeNote that you cannot make use of Bootstrap without making use of Html and CSS and if you are reading this article I will encouraged you to read my previous articles to have the basic knowledge needed before approaching the CSS Frameworks ConclusionWowI Hope and believe you have gain one or two things from this article In this fantastic series of Getting Started with Bootstrap keep an eye out for more from my blog You can also read this Article to learn more about Html and CSSYou can reach out to me on Twitter to learn more about any subject and I will respond Thank you for taking the time to read this Enjoy	2022-02-21 10:10:47
海外TECH	DEV Community	Advantages of Doubly Linked List in Data Structure	https://dev.to/scalertopics/advantages-of-doubly-linked-list-in-data-structure-3h6b	Advantages of Doubly Linked List in Data Structure IntroductionA linked list contains nodes in which each node has a data part and the reference to the next node Each node in a linked list is connected via links The operations that can be performed on a linked list are search insert delete traverse etc There are various kinds of linked lists like singly link list doubly link list and circular link list In this article we will see the most used doubly link list and its advantages What is a Doubly Linked List Doubly linked list is a variation of linked list in which we can move forward and backward We can define a doubly linked list using the following terms Link Each link of a linked list can store a data called an element Next Each link of a linked list contains a link to the next link called Next Prev Each link of a linked list contains a link to the previous link called Prev LinkedList A Linked List contains the connection link to the first link called First and to the last link called Last An example of a doubly linked list is the tabs in the browser you can move to any tab forward or backward So if a Linked List ⇒A →B →CThen a Doubly Linked List ⇒A ⇆B ⇆C Representation of a Doubly Linked List in Data StructureA class node is created that contains a data variable to hold the value of a node A next pointer to store the address of the next linked node in the list A prev pointer to store the address of previously linked nodes in the list C Codeclass Node public int data value of a node in linked list Node next Pointer to next node in DLL Node prev Pointer to previous node in DLL C Codestruct Node create a structure for C ll int data value of a node in linked list struct Node next Pointer to next node in DLL struct Node prev Pointer to previous node in DLL Operations on a Doubly Linked ListThe following are some various operations that can be performed in a doubly linked list Add a Node in the FrontSteps involved Allocate nodePut in the dataMake next of new node as head and previous as NULLChange prev of head node to new nodeMove the head to point to the new nodeAdd a Node After a Given Node Steps involved Check if the given previous node is NULL Allocate new nodePut in the data Make next of new node as next of previous nodeMake the next of previous node as new nodeMake previous node as previous of new nodeChange previous of new node s next nodeAdd a Node in the EndSteps involved Allocate node and put in the dataThis new node is going to be the last node so If the Linked List is empty then make the newElse traverse till the last nodeChange the next of last nodeMake last node as previous of new nodeAdd a Node in the EndSteps involved Check if the next node is NULL or not If it s NULL return from the function because any new node can not be added before a NULLAllocate memory for the new node let it be called new nodeSet the value of data to the new node Set the previous pointer of this new node as the previous node of the next node new node gt prev next node gt prevSet the previous pointer of the next node as the new node Set the next pointer of this new node as the next node If the previous node of the new node is not NULL then set the next pointer of this previous node as new node Else if the prev of new node is NULL it will be the new head node Code to Demonstrate the Insertion Operations CPP include lt bits stdc h gt using namespace std class Node Create a doubly linked list public int data value of a node Node next next pointer Node prev previous pointer of node void push Node head ref int new data insert a node in front of list allocate node Node new node new Node put in the data new node gt data new data Make next of new node as head and previous as NULL new node gt next head ref new node gt prev NULL change prev of head node to new node if head ref NULL head ref gt prev new node move the head to point to the new node head ref new node void insertAfter Node prev node int new data function to insert after a node check if the given prev node is NULL if prev node NULL cout lt lt the given previous node cannot be NULL return allocate new node Node new node new Node put in the data new node gt data new data Make next of new node as next of prev node new node gt next prev node gt next Make the next of prev node as new node prev node gt next new node Make prev node as previous of new node new node gt prev prev node Change previous of new node s next node if new node gt next NULL new node gt next gt prev new node void append Node head ref int new data function to add a new node at the end allocate node Node new node new Node Node last head ref used in step put in the data new node gt data new data This new node is going to be the last node so make next of it as NULL new node gt next NULL If the Linked List is empty then make the new node as head if head ref NULL new node gt prev NULL head ref new node return Else traverse till the last node while last gt next NULL last last gt next Change the next of last node last gt next new node Make last node as previous of new node new node gt prev last return void printList Node node function to print the doubly linked list Node last cout lt lt nTraversal in forward direction n while node NULL cout lt lt lt lt node gt data lt lt last node node node gt next cout lt lt nTraversal in reverse direction n while last NULL traverse the list in reverse direction cout lt lt lt lt last gt data lt lt last last gt prev int main Main function Node head NULL currently the list is empty append amp head insert in the beginning push amp head insert before push amp head Output Created Doubly linked list is Traversal in forward direction Traversal in reverse direction Deletion in Doubly Linked ListThe deletion of nodes can be divided into three categories head middle and last node deletion Steps to be performed for deletionLet the node be Deleted be D If the node to be Deleted is the head node then change the head pointer to the next current head Set next to previous to D if previous to D exists Set prev of next to D if next to D exists CPP Code to Perform Deletion Operation include lt bits stdc h gt using namespace std class Node create a doubly linked list public int data value of the node Node next next pointer of the node Node prev previous pointer to the node void deleteNode Node head ref Node del function to delete a node in DLL base case if head ref NULL del NULL return if head ref del head ref del gt next if del gt next NULL del gt next gt prev del gt prev if del gt prev NULL del gt prev gt next del gt next Finally free the memory occupied by del free del return void push Node head ref int new data function to insert data into the DLL Node new node new Node put in the data new node gt data new data new node gt prev NULL new node gt next head ref if head ref NULL head ref gt prev new node head ref new node void printList Node node function to print the content of the DLL while node NULL iterate till the end of DLL cout lt lt node gt data lt lt print node data node node gt next int main main function Node head NULL currently head is NULL DLL created lt gt lt gt lt gt push amp head push amp head push amp head push amp head cout lt lt Original Doubly Linked list printList head print original DLL delete nodes from the doubly linked list deleteNode amp head head Output Original Doubly Linked list Modified Doubly Linked list Advantages of a Doubly Linked ListAs we have seen the operations of a DLL below are the advantages It becomes easier to iterate in both directions Deletion of a particular node is easy as we have access to the previous node Performing a reverse operation is easy A DLL can grow and shrink dynamically It is beneficial in implementing other data structures like binary trees hash tables stacks etc It provides the flexibility to perform undo redo operations It can also be used in gaming like playing deck of cards Traversing a DLL in a bidirectional manner is easy as compared to singly linked lists In the operating system a thread scheduler manages a doubly linked list of all the processes The concept of DLL can be applied in forward and backward navigation areas Disadvantages of a Doubly Linked ListIt stores an extra pointer to store the address of previously linked nodes Hence it consumes more memory when compared to a singly linked list Due to extra pointers more time is required in handling the overhead We can t randomly access elements in a doubly linked list ConclusionA doubly linked list has three parts the data next and a previous pointer We can perform various operations on a doubly linked list like add a node in front add a node in last delete a node in front delete a node in the lost insert a node after a given node insert a node before a given node etc The main benefit of a doubly linked list is its iteration in backward and forward direction Also a DLL can shrink dynamically Doubly linked list examples are a music playlist in which songs can be changed by moving backward and forward the undo and redo functionality in a word file etc Reference Scaler Topics	2022-02-21 10:06:10
海外TECH	DEV Community	Future Javascript: Records and Tuples	https://dev.to/smpnjn/future-javascript-records-and-tuples-14fk	Future Javascript Records and TuplesRecords and Tuples are an upcoming feature for Javascript which may be familiar if you have used other languages They are very similar to Arrays and Objects the key difference being that they are immutable meaning they can t be updated or changed They give us a brand new primitive type in Javascript and let us do a lot of things we couldn t previously do including comparing objects and arrays by value rather than identity In this article we ll cover how they work and how you can use them today Support for Records and TuplesCurrently records and tuples are a stage proposal for Javascript Broadly speaking this means that they are relatively stable but not implemented as a standard spec As such major browsers and backend Javascript like Node JS do not implement them You can however use them if you have Babel by using this polyfill What are Records and Tuples in Javascript Records and Tuples introduce a brand new primitive type to Javascript but ultimately follow the same syntax as Objects and Arrays When we want to define a new Record or Tuple we use the syntax or As such we can define both as shown in the code below let myRecord name New Record tags some tags go here let myTuple some other set of array items As you can see the syntax is identical to objects and arrays with the exception of the hash at the start Note that we can also put a Tuple in our Record as shown in the first example Records and Tuples are immutableBoth Records and Tuples in Javascript are deeply immutable All that means is that they can t be changed at any level If you try to change them you ll get an error let myRecord name New Record tags some tags go here myRecord name Another Record This will throw an errorThat also means you can t insert something new into them In that way they act as a source of truth which brings us onto their main use case Both Tuples and Records allow us to compare Objects and Arrays based on their value rather than their identity Records and Tuples compare Values not IdentityIf you try to run the following code you ll get false back console log a a returns falseconsole log returns falseThat might be confusing but it s because equality of Objects and Arrays work on the basis of identity When we define a new Object or Array it is given a unique identity As such when comparing the identity of two different Objects the result is false Records and Tuples break that convention and allow us to compare by value Deep comparisons of objects has been something that s been quite tricky in Javascript for a long time but with Tuples and Records we can finally do that As such the following code returns true console log a b a b return trueconsole log returns trueThis means we can finally and easily make comparisons of the value between different objects where we expect a very specific return value Converting Arrays to Tuples and Objects to Records in JavascriptSince Records and Tuples are compared by value you may want to convert regular Objects and Arrays into them so that you can make that comparison Fortunately we can convert any Object or Array into a Record or Tuple using Record and Tuple let newRecord Record a b let newTuple Tuple let anotherTuple Tuple from Both the above lines will produce the Record and Tuple version of each Future proposals also include a JSON parseImmutable function which will let us convert strings of Arrays or Objects straight into their Tuple or Record form This is not currently implemented Adding to a Tuple or RecordI am aware that I have just said that you can t add or change to a Tuple or Record but you can produce a new Tuple or Record based on an old one This will be a totally different Tuple Record but it will use the data from the old and add something new We can do that as shown below let myTuple let myRecord a b Produce a new record using original myRecord let newRecord myRecord c a b c Produce a new tuple using myTuple let newTuple myTuple Or you can use Tuple with let anotherTuple myTuple with Interacting with Tuples and Records in JavascriptTuples and Records work exactly the same as Objects and Arrays except they cannot be changed As such you can iterate through them or interact with them using the same methods as are available on Objects and Arrays For example we could get all the keys of a particular Record let myRecord a b c let recordKeys Object keys myRecord Returns a b c Or you could iterate over an array using a for loop let myTuple for const i of myTuple console log i Console logs on after each other ConclusionAs Tuples and Records aren t widely supported you will need the Babel polyfill to use them They allow us to compare data from Objects and Arrays in ways we couldn t before making code much simpler where it once required complicated custom functions To read the full proposal click here	2022-02-21 10:05:29
Apple	AppleInsider - Frontpage News	Donald Trump's 'Truth Social' launches app	https://appleinsider.com/articles/22/02/21/donald-trumps-truth-social-launches-app?utm_medium=rss	Donald Trump x s x Truth Social x launches appIntended to rival Twitter Donald Trump s Truth Social platform is now available in the App Store though users report errors and problems creating accounts Following Twitter Facebook and Instagram banning the former president from their platforms Trump is launching his own Despite Truth Social reportedly being delayed until March however the new service launched its app on the App Store on Sunday February According to CNET early users have complained about error messages while trying to create their accounts Forbes magazine says some users successfully created an account but were then told they are on a waitlist due to massive demand Read more	2022-02-21 10:42:38
Apple	AppleInsider - Frontpage News	Apple gives Oscar nominated 'CODA' movie a theatrical re-release, for free	https://appleinsider.com/articles/22/02/18/apple-gives-oscar-nominated-coda-movie-a-theatrical-re-release-for-free?utm_medium=rss	Apple gives Oscar nominated x CODA x movie a theatrical re release for freeApple TV film CODA is returning to theaters for a limited run of free screenings to celebrate its Best Picture Oscar nomination CODA scored three nominations at the th Academy Awards It got nods for best adapted screenplay for writer director Sian Heder and best actor in a supporting role for Troy Kotsur Now according to Deadline audiences are going to get to see the film back in theaters Read more	2022-02-21 10:08:04
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海外TECH	reddit	二階派、片山さつき氏に退会勧告「信用著しく失う」	https://www.reddit.com/r/newsokuexp/comments/sxq0zl/二階派片山さつき氏に退会勧告信用著しく失う/	tornewsokuexplinkcomments	2022-02-21 10:03:47