Algorithms

Sorting Algorithm

 https://www.geeksforgeeks.org/radix-sort/

https://www.geeksforgeeks.org/heap-sort/

Dynamic Programming - Optimization of the solution.

1. Greedy Algorithm  - In a greedy algorithm the decision is taken once and the result is calculated based on the same decision. Like Dijastra's Algorithm where we always take the shortest vertex to find the shortest path. Other example Minimum cost spanning tree - Always select the minimum cost edge.

2. Dynamic Programming - The decision is taken at every step to get to an optimal solution.

Memoization  is a technique used to optimize the time complexity. In the technique we store the result of the calculation so that we can use them again. It is a top down approach. This is used in Recursion.

Tabulation is a technique which is a bottom up approach. We start with the smallest value and calculate the bigger problems. It is used as part of the iterative method

Software Architectural Patterns

 

Architectural Patterns

1. Layered pattern
2. Client-server pattern
3. Master-slave pattern
4. Pipe-filter pattern
5. Broker pattern
6. Peer-to-peer pattern
7. Event-bus pattern
8. Model-view-controller pattern
9. Blackboard pattern
10. Interpreter pattern

Hexagonal Architecture

Onion Architecture

Layered Architecture

Domain Driven Design

Domain-Driven Design is about creating shared understanding of the problem space that is reinforced ubiquitously via conversations, code and diagrams.
Things to know in Domain Driven Design 

1. What is Bounded Context ?
   Bounded context defines tangible boundaries of applicability of some sub-domain. It is an area where a certain sub-domain makes sense, while the others don't. It can be a talk, a presentation, a code project with physical boundaries defined by the artifact.
   
   
2. What is Ubiquitous Language ?
   A Bounded Context is an explicit boundary within which a domain model exists. Inside the boundary all terms and phrases of the Ubiquitous Language have specific meaning, and the model reflects the Language with exactness.

Event Driven Design

Reactive Architecture

https://www.lightbend.com/blog/understand-reactive-architecture-design-and-programming-in-less-than-12-minutes

Reference

• https://towardsdatascience.com/10-common-software-architectural-patterns-in-a-nutshell-a0b47a1e9013
• https://medium.com/@edamtoft/onion-vs-clean-vs-hexagonal-architecture-9ad94a27da91
• https://www.codeguru.com/csharp/understanding-onion-architecture/

Network Layer

 Websockets vs HTTP

WebSockets, on the other hand, allow for sending message-based data, similar to UDP, but with the reliability of TCP. WebSocket uses HTTP as the initial transport mechanism, but keeps the TCP connection alive after the HTTP response is received so that it can be used for sending messages between client and server.

https://sookocheff.com/post/networking/how-do-websockets-work/#:~:text=WebSockets%2C%20on%20the%20other%20hand,messages%20between%20client%20and%20server.

Network Layer

Capacity Estimation and Planning

 1 Byte = 8 bits

1 byte = 1 ASCII character. 

2 bytes = 1 UTF-16

UTF-8

UTF-8 is based on 8-bit code units. Each character is encoded as 1 to 4 bytes.

2^32  = 4,294,967,296

1 KB = 1000 Bytes

1 MB = 1000 KB

1 GB = 1000 MB

1 TB = 1000 GB

1 PB = 1000TB 

1 Million = 1,000,0000 = 10^6

1 Billion = 1,000,000,000 = 10^9

1 Trillion = 1,000,000,000,000 = 10^12

Request Calculation per second

1 M req per day = 1 M req / 86400 seconds = 12 req per second

1.5 M req per day = 1.5 * (1 M req / 86400 seconds) = 18 req per second

10 M req per day = 10 M req / 86400 seconds = 120 req per second

1 B req per day = 1B req / 86400 seconds = 12000 req per second

Redis can handle 81000 req per second

Number of users
Twitter users = 300 million active monthly users

Youtube = 2 Billion active monthly users
Number of videos watched per day = 5 billion

Facebook users 3 billion users out of which 2 billion are daily active users

Pastebin users = 17 million

Bitly = 600 million bitly link created per month.

Name	Length
char	1 byte
short	2 bytes
int	4 bytes
long	4 bytes
float	4 bytes
double	8 bytes
long double	16 bytes Note that on AIX® and Linux® PPC a long double is 8 bytes.
pointer	4 bytes
ptrdiff_t	4 bytes
size_t	4 bytes
time_t	4 bytes
clock_t	4 bytes

Videos :

Design Principles and Design Pattern

 Design Principles

• Encapsulate what varies
• Favor Composition over Inheritance
• Loose Coupling
• Program to interfaces
• SOLID Principle
• Single Responsibility Principle
• Open/Closed Principle
• Liskov's substitution principle
• Interface Segregation Principle
• Dependency Inversion Principle.

   Design Patterns

• Creational Design Pattern
• Factory Pattern - 
  Let the factory do the job of creating the objects rather than instantiating the object using New
  https://java-design-patterns.com/patterns/factory/ 
• Abstract Factory Pattern -
  Creating a Factory from list of factories.
  https://java-design-patterns.com/patterns/abstract-factory/
• Builder Pattern - 
  The builder pattern is an object creation software design pattern with the intentions of finding a solution to the telescoping constructor anti-pattern. Telescoping constructor anti-pattern means that the constructor is getting bigger and bigger due to addition of a lot of parameters.
  https://java-design-patterns.com/patterns/builder/
• Prototype Pattern - Clone the existing object and then make modification to the object rather than creating the object from scratch.
  https://java-design-patterns.com/patterns/prototype/
  In java can be done by implementing the Cloneable  and overriding the Clone() method. But Clonable makes a shallow copy. We need to override the clone method for the child objects and the clonable method should be updated
• Singleton Pattern
  

Restful Services

https://www.softwaretestinghelp.com/restful-web-services-interview-question/

https://restfulapi.net/caching/

Microservices Design Patterns : https://vslive.com/Blogs/News-and-Tips/2018/02/Go-Fast-by-Going-Micro-Microservices-Design-Patterns-You-Should-Know.aspx

http://blog.arungupta.me/microservice-design-patterns/

https://www.edureka.co/blog/microservices-design-patterns

Authentication & Authorization : https://medium.com/tech-tajawal/microservice-authentication-and-authorization-solutions-e0e5e74b248a

Learn to be a backend Developer : https://medium.com/tech-tajawal/modern-backend-developer-in-2018-6b3f7b5f8b9

Design Steps

• Identify object model
• Create Model URIs
• Determine Representations
• Assign HTTP Methods

JAX-RS 2.0 (Java API for RESTful Services).

JAX-RS stands for JAVA API for RESTful Web Services

From <https://www.tutorialspoint.com/restful/restful_jax_rs.htm>

From <https://restfulapi.net/create-rest-apis-with-jax-rs-2-0/>

Caching

https://www.tutorialspoint.com/restful/restful_caching.htm

Has the following attributes in the header

• Date
• Last Modified
• Cache Control - Public, Private, no-cache/no-store, max-age, must-revalidate
• Expires
• Age

1. Scope microservices using Bounded Context
1. Domain Driven Design- Bounded Context
2. Ubiquitous Language
2. N+1 problem - https://restfulapi.net/rest-api-n-1-problem/
3. Asynchronous Web Services - Event Based
1. Competing Worker Pattern
2. Fanout Pattern
3. Async API Call
4. Architecture of API Based Microservice
1. Functional Requirement
1. Loosely coupled
2. Independently changeable
3. Independently deployable
4. Support and honor contracts
5. Technology Agnostic
6. Stateless API
2. API Architectural Styles
1. Basic REST Implementation
1. Following the rest constraints
2. HTTP Protocol is followed
3. Inherits the advantages of the Web
4. Uses JSON/XML to send and receive data
5. Uses Resource End point to communicate
6. Uniform Resource Identifier
7. Stateless
8. Cacheable
9. Example
   
2. Pragmatic REST
1. Not all resources would do CRUD Operation
2. Some resources takes actions/Task
3. Name these resources as Verbs instead of nouns
3. HATEOAS REST
4. RPC
5. SOAP
3. API Architectural Pattern
1. Façade Pattern
1. Proxy Pattern
1. Stateless service pattern

1. No State information maintained on server
2. Clients maintain state
3. State is send as part of the request
4. Advantages: Help in scalability, performance and availability

5. Composing Microservices
1. Composition Patterns
1. Broker Composition Pattern
2. Aggregate Composition Pattern
3. Chained Composition Pattern
4. Proxy Composition Pattern
5. Branch Composition Pattern

Data Consistency

1. Two Phase Commit
2. Saga Pattern-Saga Execution Coordinator

3. Eventual Consistency : Eventually the Data would be consistent across the systems. It is a practice rather than pattern. It chooses Availability over Consistency.

API Gateway

Open Source API Gateway

https://konghq.com/

Google Interview Guide

 Engineering Manager Interview Guide

https://igotanoffer.com/blogs/tech/google-engineering-manager-interview 

Google Behavioural Questions Guide

https://igotanoffer.com/blogs/tech/google-behavioral-interview

https://igotanoffer.com/blogs/tech/google-engineering-manager-interview

Google Interview Guide
https://cdn.shopify.com/s/files/1/0417/7869/files/GoogleManager.pdf?v=1590400847

Some useful Links for preparation.

• Hired in Tech

• How to approach System design interview questions

• Building large-scale distributed systems (video version) 

• The Google File System

• Bigtable: A Distributed Storage System for Structured Data

Code Review

https://github.com/google/eng-practices/blob/master/review/reviewer/index.md 

A Review - https://www.teamblind.com/post/Google-code-review-interview-5HSeJtjD

Google File System

• https://www.youtube.com/watch?v=eRgFNW4QFDc
• https://ai.google/research/pubs/pub51

• What is your mentorship style? Give a example of a employee that you helped them grow
• Have you handled any arrogant and stubborn employee ? Give Example.
• How do you keep your team motivated ?
• Have you taken an unpopular decision and how did it work out ? examples 
• Have you worked on a project with vague requirement ? How did you go about the same?
• How have you contributed to team and stepped up when the team needed me.
• How do you create visibility for the team?
• Tell me about a time you led a team through a difficult situation
• How would you build a diverse and inclusive team
• Tell me a time when you failed or made a big mistake

General

• Why are you an effective R&D leader?
• Tell me about yourself
• Why Google?

People management

• How do you handle conflicts?
• How do you handle people who are not team players?
• How do you deal with low performers?
• How do you deal with high performers? 
• Tell me about a time you developed and retained team members
• How do you manage your team’s career growth?
• Tell me about a difficult employee situation that you handled well/not so well
• What would you do with someone that had stayed at the same level for too long?
• How do you recruit good engineers?
• Give an example of how you helped another employee
• Tell me about a time you had a conflict with your supervisor and how you resolved it

Project management

• As a manager, how do you handle trade-offs?
• Describe how you deal with change management
• Describe in detail a project that failed
• Describe a project in the past that was behind schedule and provide concrete to steps that you took to remedy the situation
• Tell me how you would balance engineering limitations with customer requirements
• What was the largest project you've executed?
• Tell me about a time you needed to deliver a project on a deadline but there were multiple roadblocks and constraints to deliver. How did you manage that situation?
• Tell me about a project, product or system you worked upon. What were the design and technical problems you faced? How did you solve them?