System Design Interview Checklist:

Usually, the System Design interviews are lengthy and cover a lot of complex components. This makes it very easy to get lost in small things and miss out on the big picture. Therefore, it becomes very important to structure your interview in a way such that you can easily convey the whole picture without wasting time on anything which does not add value.

Drive the interview:

Make sure you are the one driving the interview and not your interviewer. This does not mean that you do not let them speak, but rather, you should be the one doing most of the talking, proactively calling out issues in your design before the interviewer points it out, handle the edge cases that the interviewer might poke you on etc.

FRs and NFRs:

Clearly call out the Functional and Non-Functional requirements. The intent is that the requirements should be big enough that makes the problem challenging and also finite enough that you can build a system that fulfills those requirements within the stipulated time. From the Non Functional side, try to make a system that works at a very large scale. What’s the fun in designing a system which works at a low scale? Before finalizing the FRs and the NFRs, get them reviewed with your interviewer to make sure they do not want to add/ remove something. At times, interviewers do have some particular use cases in mind that they want to go over.

Capacity Estimation:

Check with your interviewer if they want to get into this. A lot of people prefer to skip the calculations and focus more on the design, assuming a large enough approximate number for the number of cores required or the amount of disk required etc.

Plan:

Based on the FRs and NFRs, come up with these things: User Interaction Points. Latency/ Availability/ Consistency requirements at each of the user interaction points. A quick analysis estimating if it’s a read-heavy interaction or a write-heavy interaction. Based on the above three, come up with what all services you’ll need and what kind of databases you can use to store the data that each of these services owns.

HLD:

Come up with a high level component diagram, that covers the following: What all services are present? Make sure you divide the flow into multiple functional components and see if a microservices based approach makes sense or not. Usually, using a microservices based approach is a good idea in SD interviews. How do the services interact with each other and what kind of protocols are used for inter service communication like Async/ Sync — Rest, RPC etc? How would the users interact with the whole system and what all services are user facing. Do you need a Cache to reduce latencies? Which service uses what Database and why? You can refer to this video that can help you choose the right database based on your use case See if you need caching anywhere and if you do, then what shall be the eviction policy, do you need an expiry for the keys, should it be a write through cache etc? Basis all this analysis, draw out a High Level Diagram of your whole system.

Must Haves:

Some key things your high level diagram should have are: Load Balancers Services Databases and Caches User interaction points Any other tools like a Message Queue, CDN, etc.

Walkthrough the design:

Once you have the whole diagram ready, go over the whole design, one use case at a time and explain your design to your interviewer at a very high level. Talk about why you have chosen a particular database here and why you have used a particular mode of communication like Sync/ Async etc. You can also get into an RPC vs HTTP kind of a conversation if you made a particular design choice. You should go over what kind of data replication strategy is being used in your databases, for example, would you use a Master-Slave or a Multi Master setup etc.

CAUTION:

Do not go into the details like APIs, DB Schema etc right away unless the interviewer asks for it. Most people get lost in designing the APIs for just one system at this point and run out of time later on. Brownie Points: Most interviews do not have FRs and NFRs around analytics, but if your design covers that or leaves good enough scope for analytics, that elevates your solution a lot.

Implementation:

Once you explain the whole flow to your interviewer, ask them which component they want to discuss in detail. Usually, people do not want to go over the entire system in detail. Let them decide which is that one component that they want to dig into and then you can go over the implementation details of that particular system.

Things you should cover here are:

APIs — Call out the APIs that this system exposes. Make sure you are using the best practices here. For example instead of a GET API with URL like GET /user/getUserbyUserId, it’s better to use: GET /user/{id} API Protocols — You can cover what protocols are you exposing the APIs on. Most people choose REST APIs, but you can decide to use something more efficient like Thrift, Protobuf etc based on your use cases. Events — You can call out which events this particular service listens to, who produces that event, what payload comes in, what processing happens on that event etc.

DB Schema:

Go over the DB Schema here. You can also get into SQL vs NoSQL debate or why have you chosen a particular database, if you did not go over the same earlier while talking about the high level design. If it’s a SQL, do talk about what indices you’ll have and how are you optimising your queries. In case of NoSQL, make sure you go over the consistency guarantees that the DB provides, can it cause any issues and the kind of queries you’ll run on that DB. Clearly call out the keys for key-value stores or the partition keys for a columnar store etc.

Handle Murphy’s law:

This is something that most people skip but this is one of the most important things that you must cover which talks about how resilient your system is. In the real world, things break, and when they do, you need to make sure you are in full control of your system. Talk about how you monitor the system. What kind of alerting mechanism do you have in place? What are your KPIs (Key Performance Indicators) and how do you track them? What happens when things break, when your service crashes, your DB’s master node goes down or even when one of your datacentres goes down?

Well this was for System Design, if you want to look at how was I able to crack companies like Google, Facebook, Amazon, etc, have a look at my Overall preparation strategy at: Hope this helps!

Table:

#	Title	Tag

| 1 | Airbnb | Airbnb |

| 2 | Amazon | Amazon |

| 3 | Facebook | Facebook |

| 4 | Google Maps | Google Maps |

| 5 | Hotel Booking | Hotel Booking |

| 6 | Notification Service | Notification Service |

| 7 | Twitter | Twitter |

| 8 | Uber System | Uber System |

| 9 | Video Streaming | Video Streaming |

| 10 | Whatsapp | Whatsapp |

| 11 | Zoom | Zoom |

System Design Cheatsheet:

Picking the right architecture = Picking the right battles + Managing trade-offs

Basic Steps:

Clarify and agree on the scope of the system

User cases (description of sequences of events that, taken together, lead to a system doing something useful)
- Who is going to use it?
- How are they going to use it?
Constraints
- Mainly identify traffic and data handling constraints at scale.
- Scale of the system such as requests per second, requests types, data written per second, data read per second)
- Special system requirements such as multi-threading, read or write oriented.

High level architecture design (Abstract design)

Sketch the important components and connections between them, but don't go into some details.
- Application service layer (serves the requests)
- List different services required.
- Data Storage layer
- eg. Usually a scalable system includes webserver (load balancer), service (service partition), database (master/slave database cluster) and caching systems.

Component Design

Component + specific APIs required for each of them.
Object oriented design for functionalities.
- Map features to modules: One scenario for one module.
- Consider the relationships among modules:
  - Certain functions must have unique instance (Singletons)
  - Core object can be made up of many other objects (composition).
  - One object is another object (inheritance)
Database schema design.

Understanding Bottlenecks

Perhaps your system needs a load balancer and many machines behind it to handle the user requests. * Or maybe the data is so huge that you need to distribute your database on multiple machines. What are some of the downsides that occur from doing that?
Is the database too slow and does it need some in-memory caching?

Scaling your abstract design

Vertical scaling
- You scale by adding more power (CPU, RAM) to your existing machine.
Horizontal scaling
- You scale by adding more machines into your pool of resources.
Caching
- Load balancing helps you scale horizontally across an ever-increasing number of servers, but caching will enable you to make vastly better use of the resources you already have, as well as making otherwise unattainable product requirements feasible.
- Application caching requires explicit integration in the application code itself. Usually it will check if a value is in the cache; if not, retrieve the value from the database.
- Database caching tends to be "free". When you flip your database on, you're going to get some level of default configuration which will provide some degree of caching and performance. Those initial settings will be optimized for a generic usecase, and by tweaking them to your system's access patterns you can generally squeeze a great deal of performance improvement.
- In-memory caches are most potent in terms of raw performance. This is because they store their entire set of data in memory and accesses to RAM are orders of magnitude faster than those to disk. eg. Memcached or Redis.
- eg. Precalculating results (e.g. the number of visits from each referring domain for the previous day),
- eg. Pre-generating expensive indexes (e.g. suggested stories based on a user's click history)
- eg. Storing copies of frequently accessed data in a faster backend (e.g. Memcache instead of PostgreSQL.
Load balancing
- Public servers of a scalable web service are hidden behind a load balancer. This load balancer evenly distributes load (requests from your users) onto your group/cluster of application servers.
- Types: Smart client (hard to get it perfect), Hardware load balancers ($$$ but reliable), Software load balancers (hybrid - works for most systems)

Database replication
- Database replication is the frequent electronic copying data from a database in one computer or server to a database in another so that all users share the same level of information. The result is a distributed database in which users can access data relevant to their tasks without interfering with the work of others. The implementation of database replication for the purpose of eliminating data ambiguity or inconsistency among users is known as normalization.
Database partitioning
- Partitioning of relational data usually refers to decomposing your tables either row-wise (horizontally) or column-wise (vertically).
Map-Reduce
- For sufficiently small systems you can often get away with adhoc queries on a SQL database, but that approach may not scale up trivially once the quantity of data stored or write-load requires sharding your database, and will usually require dedicated slaves for the purpose of performing these queries (at which point, maybe you'd rather use a system designed for analyzing large quantities of data, rather than fighting your database).
- Adding a map-reduce layer makes it possible to perform data and/or processing intensive operations in a reasonable amount of time. You might use it for calculating suggested users in a social graph, or for generating analytics reports. eg. Hadoop, and maybe Hive or HBase.
Platform Layer (Services)
- Separating the platform and web application allow you to scale the pieces independently. If you add a new API, you can add platform servers without adding unnecessary capacity for your web application tier.
- Adding a platform layer can be a way to reuse your infrastructure for multiple products or interfaces (a web application, an API, an iPhone app, etc) without writing too much redundant boilerplate code for dealing with caches, databases, etc.

Key topics for designing a system:

Concurrency

Do you understand threads, deadlock, and starvation? Do you know how to parallelize algorithms? Do you understand consistency and coherence?

Networking

Do you roughly understand IPC and TCP/IP? Do you know the difference between throughput and latency, and when each is the relevant factor?

Abstraction

You should understand the systems you’re building upon. Do you know roughly how an OS, file system, and database work? Do you know about the various levels of caching in a modern OS?

Real-World Performance

You should be familiar with the speed of everything your computer can do, including the relative performance of RAM, disk, SSD and your network.

Estimation

Estimation, especially in the form of a back-of-the-envelope calculation, is important because it helps you narrow down the list of possible solutions to only the ones that are feasible. Then you have only a few prototypes or micro-benchmarks to write.

Availability & Reliability

Are you thinking about how things can fail, especially in a distributed environment? Do know how to design a system to cope with network failures? Do you understand durability?

Web App System design considerations:

Security (CORS)
Using CDN
- A content delivery network (CDN) is a system of distributed servers (network) that deliver webpages and other Web content to a user based on the geographic locations of the user, the origin of the webpage and a content delivery server.
- This service is effective in speeding the delivery of content of websites with high traffic and websites that have global reach. The closer the CDN server is to the user geographically, the faster the content will be delivered to the user.
- CDNs also provide protection from large surges in traffic.
Full Text Search
- Using Sphinx/Lucene/Solr - which achieve fast search responses because, instead of searching the text directly, it searches an index instead.
Offline support/Progressive enhancement
- Service Workers
Web Workers
Server Side rendering
Asynchronous loading of assets (Lazy load items)
Minimizing network requests (Http2 + bundling/sprites etc)
Developer productivity/Tooling
Accessibility
Internationalization
Responsive design
Browser compatibility

Working Components of Front-end Architecture:

Code
- HTML5/WAI-ARIA
- CSS/Sass Code standards and organization
- Object-Oriented approach (how do objects break down and get put together)
- JS frameworks/organization/performance optimization techniques
- Asset Delivery - Front-end Ops
Documentation
- Onboarding Docs
- Styleguide/Pattern Library
- Architecture Diagrams (code flow, tool chain)
Testing
- Performance Testing
- Visual Regression
- Unit Testing
- End-to-End Testing
Process
- Git Workflow
- Dependency Management (npm, Bundler, Bower)
- Build Systems (Grunt/Gulp)
- Deploy Process
- Continuous Integration (Travis CI, Jenkins)

Links

How to rock a systems design interview

System Design Interviewing

Scalability for Dummies

Introduction to Architecting Systems for Scale

Scalable System Design Patterns

Scalable Web Architecture and Distributed Systems

What is the best way to design a web site to be highly scalable?

interviewbit

SYSTEM DESIGN PREPARATION

How to prepare for and answer system design questions

Objective

Learning about and implementing large-scale distributed system is not easy. I do not want to give the impression that it's something that can be learnt in a month. What this repository aims to achieve, is for software engineers and students to get a rough idea of how the thought process of designing a large scale works and how big companies have managed to solve really hard problems. Along with that, there is a recent trend for companies to have an open-ended interview with system design questions, which is at times hard for engineers of all levels if they haven't gotten the opportunity to work on such systems themselves.

This is a collection of links/documents for the following use cases: a) Prepare for a system design or open-ended rounds. b) Learn more about how large-scale systems work and thought process of designing a new system.

Index

Starting point

For a very broad overview please go through these lectures, really useful:

Gaurav Sen's system design series Starts from simple stuff like load balancing and message queues, then moves to building full systems like Whatsapp and Tinder.
david malans cs75 scalability talk Feel free to go through other lectures if needed.
david huffman's talk , scaling up talk (Youtube link)
scalability for dummies
Designing data intensive appliations This is by far one of the best books about large-scale systems and the practical challenges encountered during building them. It's focussed more on data-oriented applications though.

These talks should give you a starting point on how to think about such problems.

Basics

But before you begin, here are some topics(in no particular order) which in my opinion you should have a decent idea of before proceeding.

Operating system basics: how a file system, virtual memory, paging, instruction execution cycle etc work (For starters silbershatz should be enough. If you already have decent knowledge try stallings book on OS)
Networking basics: Should know the TCP/IP stack, basics of how Internet, HTTP, TCP/IP work at the minimum. cs75 on youtube (1st lecture) should give a broad overview. I personally love networking-a top down approach.
Concurrency basics: threads, processes, threading in the language you know. Locks , mutex etc.
DB basics: types of DB's (SQL vs noSQL etc ), hashing and indexing, EAV based databases, Sharding, caching for databases, master-slave etc
A basic idea of how a basic web architecture is: say load balancers, proxy, servers, Database servers, caching servers, precompute, logging big data etc. Just know broadly what is each layer for.
very basic summary of what the CAP theorem is (Have never been asked about the theorem itself, but knowing it will help you in designing large-scale systems.

How to answer in interviews

I found hiredintech videos an excellent place to start with. The way how to approach a design question as given in the link is really useful. It goes into how we start with clearing the use-cases of the system, then thinking in the abstract manner of the various component and the interactions. Think about the bottlenecks of the system and what is more critical for your system (eg latency vs reliability vs uptime etc) Address those giving the tradeoff of your approach.
system design in crack the coding interview: good approach on how to begin attacking a problem by first solving for a small usecase then expanding the system.
The best way to prepare for such questions is do mock interviews, pick any topic (given below) try to come up with a design and then go and see how and why it is designed in that manner. There is absolutely no alternative to practice!! Whiteboarding a system design question is similar to actually writing code and testing it! Just reading will only take you so far.

Steps how I approach the system design questions in interviews

These are the steps I go through mentally in the interviews, followed by actual interview experiences:

a) Be absolutely sure you understand the problem being asked, clarify on the onset rather than assuming anything
b) Use-cases. This is critical, you MUST know what is the system going to be used for, what is the scale it is going to be used for. Also, constraints like requests per second, requests types, data written per second, data read per second.
c) Solve the problem for a very small set, say, 100 users. This will broadly help you figure out the data structures, components, abstract design of the overall model.
d) Write down the various components figured out so far and how will they interact with each other.
e) As a rule of thumb remember at least these :
1. processing and servers
1. storage
1. caching
1. concurrency and communication
1. security
1. load balancing and proxy
1. CDN
1. Monetization: if relevant, how will you monetize? eg. What kind of DB (Is Postgres enough, if not why?), do you need caching and how much, is security a prime concern?
f) Special cases for the question asked. Say designing a system for storing thumbnails, will a file system be enough? What if you have to scale for facebook or google? Will a nosql based database work?
g) After I have my components in place, what I generally try to do is look for minor optimization in various places according to the use-cases, various tradeoffs that will help in better scaling in 99% cases.
h) [Scaling out or up] (http://highscalability.com/blog/2014/5/12/4-architecture-issues-when-scaling-web-applications-bottlene.html)
i) Check with the interviewer is there any other special case he is looking to solve? Also, it really helps if you know about the company you are interviewing with, what its architecture is, what will the interviewer have more interest in based on the company and what he works on?

Common Design questions

It generally depends what you are and you will be working on. Also what your level is but these are some of the more frequent interview questions.

Design amazon's frequently viewed product page (eg. which shows the last 5 items you saw)
Design an online poker game for multiplayer. Solve for persistence, concurrency, scale. Draw the ER diagram for this
Design a [url compression system] (http://www.hiredintech.com/system-design/the-system-design-process/)
Search engine (generally asked with people who have some domain knowledge): basic crawling, collection, hashing etc. Depends on your expertise on this topic
Design dropbox's architecture. good talk on this
Design a picture sharing website. How will you store thumbnails, photos? Usage of CDNS? caching at various layers etc.
- Design a news feed (eg. Facebook , Twitter): news feed
Design a product based on maps, eg hotel / ATM finder given a location.
Design malloc, free and garbage collection system. What data structures to use? decorator pattern over malloc etc.
Design a site like junglee.com i.e price comparision, availability on e-commerce websites. When and will you cache, how much to query, how to crawl efficiently over e-commerce sites, sharding of databases, basic database design
A web application for instant messaging, eg whatsapp, facebook chat. Issues of each, scaling problems, status and availability notification etc.
Design a system for collaborating over a document simultaneously (eg google docs)
(very common:) top 'n' or most frequent items of a running stream of data
Design election commission architecture : Let's say we work with the Election Commission. On Counting day, we want to collate the votes received at the lakhs of voting booths all over the country. Each booth has a voting machine, which, when connected to the network, returns an array of the form {[party_id, num_votes],[party_id_2, num_votes_2],...}. We want to collect these and get the current scores in real time. The report we need continuously is how many seats is each party leading in. Please design a system for this.
Design a logging system (For web applications, it is common to have a large number of servers running the same application, with a load balancer in front to distribute the incoming requests. In this scenario, we want to check and alarm in case an exception is thrown in any of the servers. We want a system that checks for the appearance of specific words, "Exception", "Disk Full" etc. in the logs of any of the servers. How would you design this system?)

Architectures :

Personally I looked into the following architectures:

Basics of google search
Basics of messaging frameworks like Kafka , queuing architectures like rabbitmq.
Broad overview and advantages of Redis , mongodb , cassandra.
Google file system
[Google architecture] (http://highscalability.com/google-architecture)
Instagram and other image based social networks
Memcache scaling by facebook
Twitter scaling and facebook feeds
facebook graph api
facebook haystack needle architecture
youtube architecture and optimizations for video

Company engineering blog links

courtesy checkcheckzz

Depending on where you are interviewing, go through the company blog. VERY USEFUL IN INTERVIEWS! It really helps if you have an idea of the architecture, as the questions asked will generally be of that domain and your prior knowledge will help out here.

Low on time ?

I would HIGHLY recommend you do not take a shortcut unless you have a week or so for an interview. System design is best learnt by practising, shortcuts might help you in the short term, but would recommend coming back to this link for an in-depth understanding after the interview

a) Go through cs76 and Udacity's links given above for scaling systems.
b) Go through the engineering blog of the company you are interviewing in (or if its a startup go through the link of the company closest to yours)
c) See this talk: http://www.hiredintech.com/system-design/the-system-design-process/ and develop a process for how to answer such questions.
d) Remember these terms, just roll over them in your interview in your mind, and if relevant mention it in the interview

processing and servers
storage
caching
concurrency and communication
security
load balancing and proxy
CDN
Monetization

How to prepare system design questions for an IT company

System design is a very broad topic. Even a software engineer with many years of working experience at a top IT company may not be an expert on system design. If you want to become an expert, you need to read many books, articles, and solve real large scale system design problems.

This repository only teaches you how to handle the system design interview with a systematic approach in a short time. You can dive into each topic if you have time. Of course, welcome to add your thoughts!

System Design Interview Questions

A curated list of System Design interview questions for SDE-1 (Experienced),SDE-2 and above.

All the questions have been manually curated by me from sites like Geeksforgeeks, Careercup and other interview prep sites.

Targeted companies: Amazon, Google, Facebook and other biggies.

Hope it helps you to prepare for your upcoming interviews!

Questions

Design commenting system
Design subscription based sports website which can display scores, game status, history for any games.
Design Netflix => search, video serving, authentication, encryption, dns lookup,caching strategy,serving multi quality video etc
Design a Latency Management System
Design a Library Management System
Design a Notification service
Design ESPN/Cricinfo/Cricbuzz
Design Uber
Design Whatsapp
Design Quora
Design Lookahead system
Design Google Docs/ Collaborative Editing service
Design URL Shortner service
Design RedBus
Design BookMyShow
Design Domain Backdooring system
Design Amazon Locker
Design Movies Review Aggregator System > Data should be fetched from movie rating providers like imdb, rotten tomatoes, etc
Design offline caching system for Ecommerce platform
Design Amazon E-commerce
Design Online chess game/Multiplayer game
Design gaming platform. A number of games can be hosted on this platform. User can login and select a particular game
Design a last-mile delivery platform in case of peak seasons
Design Zomato/Swiggy/Foodpanda
Design Meeting Calendar system
Design Spotify
Design Promo Code API by taking into account Amazon's customer traffic into picture
Design Vending machine with following functionalities ==> Three types of Users : User, Operator, Admin
- User can select and buy multiple items at a time. Money can be inputted multiple times (you will get the item if there is a time gap > 30 secs). He can also do window shopping (see only the prices of items and buy nothing)
- Operator can load the items and mark the items as expired if needed, gets notified if a product goes out of stock.
- Admin can own multiple vending machines, he should have a analytics report of the items purchased in a month. He can also change the prices directly and it should reflect in all the vending machines which he owns.
- Exception handling in all the edge cases
Design splitwise
Design Google pay at scale
Design a Job schedular => scalability, fault tolerance, high availability, how scheduler picks up job, how will you take care where one job can run for 30 min and one for 30 hour, how will you distribute jobs on servers. Based on frequency & time how will you execute them ? How will you notify back the user about start/stop or completion of a job ? How will your system know if a job is killed / terminated due to unknown reasons ?
Design Meeting Scheduler
Design Debugger
Design Automatic Parking System
Design a ranking system. We have an infinite supply of words ending with ‘.’ We need to implement a reader program that ranks words on the basis of certain criteria Example: This is my cat. This house belongs to my uncle An amazing country with so many tourist places And so on.. Ranking System criteria : rank the words on the basis of occurrence, for example Output : This:2, is:2, my:2… highest rank (sorted asc or desc based on provided flag) Design it completely and scalable Ranking System
Design Amazon Cart system
Design Google Search
Design Twitter
Design Facebook
Design Snapchat
Design Instagram
Design App-store
Design a music player application
Design a distributed LRU Cache
Design Gmail
Design a recommendation system
Design a food sharing application
Design payment module for Uber app
Design Truecaller type of system
Design performance management system (appraisal workflow system) that can be used across companies.
Design comment system like disqus
Design flight system
Design Tinder
Design survey site like surveymonkey
Design a geographically partitioned multi-player card game, that supports multiple players, multiple games at a time. Each game will have one contractor like ones we have in a bar, He can play a game or just watch it. Integrate payment systems
Design a kind of kindle fire application where we can subscribe news channel and read the news from all publishers as a digital format
Design a realtime Video chat like Google Duo
Design News paper & Magazine subscription system
Design a system like Hackerrank/Codechef/Topcoder
Design a concurrent Hashmap
Design an ATM Machine system which can support massive amount of transactions
Design Airport Baggage system
Design Flight Information Display system
Design a conference room booking system for a company which can have offices in multiple cities, each city can have multiple buildings, each building can have multiple floors, each floor can have multiple rooms. Each room can have features like capacitiy, video conferencing available, etc.
Design newsfeed feature of Facebook
Design an efficient Mail delivery system
Design like/dislike feature at Youtube scale.
Design Paypal
Design Air traffic control system
Design a realtime service which tells your friends who is online
Design Google Maps
Design Grammarly

Best of luck 👍, feel free to send pull requests to add more content to this git!

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Google Maps Design.png		Google Maps Design.png
Hotel Booking System.png		Hotel Booking System.png
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README.md		README.md
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Uber System Design.png		Uber System Design.png
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Whatsapp System design.png		Whatsapp System design.png
Zoom System Design.png		Zoom System Design.png
imp.txt		imp.txt
pdf.pdf		pdf.pdf

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