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Coding Interview University

Thanks to @jwasham for the wonderful work he has done in compiling all the data. I am creating a new repository with additions and deletions that helped me.

Famous LC questions for various topics

Arrays

Binary

Graph

Heap

Interval

Linked Lists

Matrix

Recursions

String

Tree

Trie

Table of Contents

---------------- Everything below this point is optional ----------------

Additional Resources

Why use it?

When I started this project, I didn't know a stack from a heap, didn't know Big-O anything, anything about trees, or how to traverse a graph. If I had to code a sorting algorithm, I can tell ya it wouldn't have been very good. Every data structure I've ever used was built into the language, and I didn't know how they worked under the hood at all. I've never had to manage memory unless a process I was running would give an "out of memory" error, and then I'd have to find a workaround. I've used a few multidimensional arrays in my life and thousands of associative arrays, but I've never created data structures from scratch.

It's a long plan. It may take you months. If you are familiar with a lot of this already it will take you a lot less time.

How to use it

How to use it

Everything below is an outline, and you should tackle the items in order from top to bottom.

I'm using Github's special markdown flavor, including tasks lists to check progress.

Create a new branch so you can check items like this, just put an x in the brackets: [x]

Fork a branch and follow the commands below

git checkout -b progress

git remote add jwasham https://github.com/jwasham/coding-interview-university

git fetch --all

Mark all boxes with X after you completed your changes

git add .

git commit -m "Marked x"

git rebase jwasham/master

git push --force

More about Github-flavored markdown

Don't feel you aren't smart enough

About Video Resources

Some videos are available only by enrolling in a Coursera or EdX class. These are called MOOCs. Sometimes the classes are not in session so you have to wait a couple of months, so you have no access.

I'd appreciate your help to add free and always-available public sources, such as YouTube videos to accompany the online course videos.
I like using university lectures.

Interview Process & General Interview Prep

Interview Process & General Interview Prep

Pick One Language for the Interview

You can use a language you are comfortable in to do the coding part of the interview, but for large companies, these are solid choices:

  • C++
  • Java
  • Python

You need to be very comfortable in the language and be knowledgeable.

Read more about choices:

See language resources here

You'll see some C, C++, and Python learning included below, because I'm learning. There are a few books involved, see the bottom.

Book List

This is a shorter list than what I used. This is abbreviated to save you time.

Interview Prep

If you have tons of extra time:

Computer Architecture

  • Write Great Code: Volume 1: Understanding the Machine

    • The book was published in 2004, and is somewhat outdated, but it's a terrific resource for understanding a computer in brief.

    • The author invented HLA, so take mentions and examples in HLA with a grain of salt. Not widely used, but decent examples of what assembly looks like.

    • These chapters are worth the read to give you a nice foundation:

      ......
      • Chapter 2 - Numeric Representation
      • Chapter 3 - Binary Arithmetic and Bit Operations
      • Chapter 4 - Floating-Point Representation
      • Chapter 5 - Character Representation
      • Chapter 6 - Memory Organization and Access
      • Chapter 7 - Composite Data Types and Memory Objects
      • Chapter 9 - CPU Architecture
      • Chapter 10 - Instruction Set Architecture
      • Chapter 11 - Memory Architecture and Organization
If you have more time (I want this book):

Language Specific

You need to choose a language for the interview (see above). Here are my recommendations by language. I don't have resources for all languages. I welcome additions.

If you read though one of these, you should have all the data structures and algorithms knowledge you'll need to start doing coding problems. You can skip all the video lectures in this project, unless you'd like a review.

Additional language-specific resources here.

C++

C++

I haven't read these two, but they are highly rated and written by Sedgewick. He's awesome.

If you have a better recommendation for C++, please let me know. Looking for a comprehensive resource.

Java

Java

OR:

  • Data Structures and Algorithms in Java
    • by Goodrich, Tamassia, Goldwasser
    • used as optional text for CS intro course at UC Berkeley
    • see my book report on the Python version below. This book covers the same topics.

Python

Python

Optional Books

Some people recommend these, but I think it's going overboard, unless you have many years of software engineering experience and expect a much harder interview:

Optional Books

  • Algorithm Design Manual (Skiena)

    • As a review and problem recognition
    • The algorithm catalog portion is well beyond the scope of difficulty you'll get in an interview.
    • This book has 2 parts:
      • class textbook on data structures and algorithms
        • pros:
          • is a good review as any algorithms textbook would be
          • nice stories from his experiences solving problems in industry and academia
          • code examples in C
        • cons:
          • can be as dense or impenetrable as CLRS, and in some cases, CLRS may be a better alternative for some subjects
          • chapters 7, 8, 9 can be painful to try to follow, as some items are not explained well or require more brain than I have
          • don't get me wrong: I like Skiena, his teaching style, and mannerisms, but I may not be Stony Brook material.
      • algorithm catalog:
        • this is the real reason you buy this book.
        • about to get to this part. Will update here once I've made my way through it.
    • Can rent it on kindle
    • Answers:
    • Errata

  • Introduction to Algorithms

    • Important: Reading this book will only have limited value. This book is a great review of algorithms and data structures, but won't teach you how to write good code. You have to be able to code a decent solution efficiently.
    • aka CLR, sometimes CLRS, because Stein was late to the game

  • Programming Pearls

    • The first couple of chapters present clever solutions to programming problems (some very old using data tape) but that is just an intro. This a guidebook on program design and architecture, much like Code Complete, but much shorter.

  • "Algorithms and Programming: Problems and Solutions" by Shen

    • A fine book, but after working through problems on several pages I got frustrated with the Pascal, do while loops, 1-indexed arrays, and unclear post-condition satisfaction results.
    • Would rather spend time on coding problems from another book or online coding problems.

Before you Get Started

This list grew over many months, and yes, it kind of got out of hand.

Here are some mistakes I made so you'll have a better experience.

1. You Won't Remember it All

I watched hours of videos and took copious notes, and months later there was much I didn't remember. I spent 3 days going through my notes and making flashcards so I could review.

Read please so you won't make my mistakes:

Retaining Computer Science Knowledge

2. Use Flashcards

To solve the problem, I made a little flashcards site where I could add flashcards of 2 types: general and code. Each card has different formatting.

I made a mobile-first website so I could review on my phone and tablet, wherever I am.

Make your own for free:

Keep in mind I went overboard and have cards covering everything from assembly language and Python trivia to machine learning and statistics. It's way too much for what's required.

Note on flashcards: The first time you recognize you know the answer, don't mark it as known. You have to see the same card and answer it several times correctly before you really know it. Repetition will put that knowledge deeper in your brain.

An alternative to using my flashcard site is Anki, which has been recommended to me numerous times. It uses a repetition system to help you remember. It's user-friendly, available on all platforms and has a cloud sync system. It costs $25 on iOS but is free on other platforms.

My flashcard database in Anki format: https://ankiweb.net/shared/info/25173560 (thanks @xiewenya)

3. Review, review, review

I keep a set of cheat sheets on ASCII, OSI stack, Big-O notations, and more. I study them when I have some spare time.

Take a break from programming problems for a half hour and go through your flashcards.

4. Focus

There are a lot of distractions that can take up valuable time. Focus and concentration are hard.

What you won't see covered

These are prevalent technologies but not part of this study plan:

  • SQL
  • Javascript
  • HTML, CSS, and other front-end technologies

Crafting Interpreters

The Daily Plan

Some subjects take one day, and some will take multiple days. Some are just learning with nothing to implement.

Each day I take one subject from the list below, watch videos about that subject, and write an implementation in:

  • C - using structs and functions that take a struct * and something else as args.
  • C++ - without using built-in types
  • C++ - using built-in types, like STL's std::list for a linked list
  • Python - using built-in types (to keep practicing Python)
  • and write tests to ensure I'm doing it right, sometimes just using simple assert() statements
  • You may do Java or something else, this is just my thing.

You don't need all these. You need only one language for the interview.

Why code in all of these?

  • Practice, practice, practice, until I'm sick of it, and can do it with no problem (some have many edge cases and bookkeeping details to remember)
  • Work within the raw constraints (allocating/freeing memory without help of garbage collection (except Python))
  • Make use of built-in types so I have experience using the built-in tools for real-world use (not going to write my own linked list implementation in production)

I may not have time to do all of these for every subject, but I'll try.

You can see my code here:

You don't need to memorize the guts of every algorithm.

Write code on a whiteboard or paper, not a computer. Test with some sample inputs. Then test it out on a computer.

Prerequisite Knowledge

Prerequisite Knowledge

Algorithmic complexity / Big-O / Asymptotic analysis

Algorithmic complexity / Big-O / Asymptotic analysis

Data Structures

Data Structures

More Knowledge

More Knowledge

Trees

Trees

Sorting

Sorting

As a summary, here is a visual representation of 15 sorting algorithms. If you need more detail on this subject, see "Sorting" section in Additional Detail on Some Subjects

Graphs

Graphs

Graphs can be used to represent many problems in computer science, so this section is long, like trees and sorting were.

You'll get more graph practice in Skiena's book (see Books section below) and the interview books

Even More Knowledge

Even More Knowledge

System Design, Scalability, Data Handling

System Design, Scalability, Data Handling

Final Review

Final Review 
This section will have shorter videos that you can watch pretty quickly to review most of the important concepts.
It's nice if you want a refresher often.

Coding Question Practice

Coding Question Practice

Now that you know all the computer science topics above, it's time to practice answering coding problems.

Coding question practice is not about memorizing answers to programming problems.

Why you need to practice doing programming problems:

  • problem recognition, and where the right data structures and algorithms fit in
  • gathering requirements for the problem
  • talking your way through the problem like you will in the interview
  • coding on a whiteboard or paper, not a computer
  • coming up with time and space complexity for your solutions
  • testing your solutions

There is a great intro for methodical, communicative problem solving in an interview. You'll get this from the programming interview books, too, but I found this outstanding: Algorithm design canvas

No whiteboard at home? That makes sense. I'm a weirdo and have a big whiteboard. Instead of a whiteboard, pick up a large drawing pad from an art store. You can sit on the couch and practice. This is my "sofa whiteboard". I added the pen in the photo for scale. If you use a pen, you'll wish you could erase. Gets messy quick.

my sofa whiteboard

Supplemental:

Read and Do Programming Problems (in this order):

See Book List above

Coding exercises/challenges

Coding Question Practice

Once you've learned your brains out, put those brains to work. Take coding challenges every day, as many as you can.

Coding Interview Question Videos:

Challenge sites:

Challenge repos:

Mock Interviews:

Once you're closer to the interview

Your Resume

  • See Resume prep items in Cracking The Coding Interview and back of Programming Interviews Exposed

Be thinking of for when the interview comes

Think of about 20 interview questions you'll get, along with the lines of the items below. Have 2-3 answers for each. Have a story, not just data, about something you accomplished.

  • Why do you want this job?
  • What's a tough problem you've solved?
  • Biggest challenges faced?
  • Best/worst designs seen?
  • Ideas for improving an existing product.
  • How do you work best, as an individual and as part of a team?
  • Which of your skills or experiences would be assets in the role and why?
  • What did you most enjoy at [job x / project y]?
  • What was the biggest challenge you faced at [job x / project y]?
  • What was the hardest bug you faced at [job x / project y]?
  • What did you learn at [job x / project y]?
  • What would you have done better at [job x / project y]?

Have questions for the interviewer

Some of mine (I already may know answer to but want their opinion or team perspective):
  • How large is your team?
  • What does your dev cycle look like? Do you do waterfall/sprints/agile?
  • Are rushes to deadlines common? Or is there flexibility?
  • How are decisions made in your team?
  • How many meetings do you have per week?
  • Do you feel your work environment helps you concentrate?
  • What are you working on?
  • What do you like about it?
  • What is the work life like?

Here are some good questions to ask at the end of the interview, extracted from various sources. The ones in bold are the ones that tend to make the interviewer go "That's a good question" and pause and think for a bit.

General

  • What are you most proud about in your career so far?
  • What is the most important/valuable thing you have learnt from working here?
  • How do your clients and customers define success?
  • What would you change around here if you could?
  • What are some weaknesses of the organization?
  • What does a typical day look like for you?
  • What do you think the company can improve at?
  • How would you see yourself growing at this company in the next few years?
  • Was there a time where you messed up and how was it handled?
  • Why did you choose to come to this company?
  • When you were last interviewing, what were some of your other options, and what made you choose this company?
  • What was something you wish someone would have told you before you joined?
  • What was your best moment so far at the company?

Culture

  • What is the most frustrating part about working here?
  • What is unique about working at this company that you have not experienced elsewhere?
  • What is something you wish were different about your job?
  • How will the work I will be doing contribute to the organization's mission?
  • What do you like about working here?
  • What is your policy on working from home/remotely?
  • (If the company is a startup) When was the last time you interacted with a founder? What was it regarding? Generally how involved are the founders in the day-to-day?
  • Does the company culture encourage entrepreneurship? Could you give me any specific examples?

Technical

These questions are suitable for any technical role.

  • What are the engineering challenges that the company/team is facing?
  • What has been the worst technical blunder that has happened in the recent past? How did you guys deal with it? What changes were implemented afterwards to make sure it didn't happen again?
  • What is the most costly technical decision made early on that the company is living with now?
  • What is the most fulfilling/exciting/technically complex project that you've worked on here so far?
  • I do / don't have experience in domain X. How important is this for me to be able to succeed?
  • How do you evaluate new technologies? Who makes the final decisions?
  • How do you know what to work on each day?
  • How would you describe your engineering culture?
  • How has your role changed since joining the company?
  • What is your stack? What is the rationale for/story behind this specific stack?
  • Do you tend to roll your own solutions more often or rely on third party tools? What's the rationale in a specific case?
  • How does the engineering team balance resources between feature requests and engineering maintenance?
  • What do you measure? What are your most important product metrics?
  • What does the company do to nurture and train its employees?
  • How often have you moved teams? What made you join the team you're on right now? If you wanted to move teams, what would need to happen?
  • What resources does the company have for new hires to study its product and processes? Are there specifications, requirements, documentation?
  • There's "C++" (or Python, Swift or any other tech) in the job description. How will you estimate my proficiency in this tech in 3 months?
  • How do you think my expertise would be relevant to this team? What unique value can I add?

Product

  • Tell me about the main products of your company.
  • What is the current version of product? (If it is v1.0 or similar - there could be a lot of chaos to work with)
  • What products are your main competitors?
  • What makes your product competitive?
  • When are you planning to provide the next release? (If in several months, it would mean a lot of requirements specified in job description are not needed right now)
  • Is the team growing, and what sort of opportunities will there be in the next year/3 years?
  • What are your highest priorities right now? For example, new features, new products, solidifying existing code, reducing operations overhead?

Management

These questions are suitable for asking Engineering Managers, especially useful for the Team Matching phase of Google interviews or post-offer calls that your recruiters set up with the various team managers.

  • How do you train/ramp up engineers who are new to the team?
  • What does success look like for your team/project?
  • What qualities do you look out for when hiring for this role?
  • What are the strengths and weaknesses of the current team? What is being done to improve upon the weaknesses?
  • Can you tell me about a time you resolved an interpersonal conflict?
  • How did you become a manager?
  • How do your engineers know what to work on each day?
  • What is your team's biggest challenge right now?
  • How do you measure individual performance?
  • How often are 1:1s conducted?
  • What is the current team composition like?
  • What opportunities are available to switch roles? How does this work?
  • Two senior team members disagree over a technical issue. How do you handle it?
  • Have you managed a poor performer at some point in your career before? What did you do and how did it work?
  • Where do you spend more of your time, high performers or low performers?
  • Sometimes there's a trade-off between what's best for one of your team members and what's best for the team. Give an example of how you handled this and why.
  • Give an example of a time you faced a difficult mentoring/coaching challenge. What did you do and why?
  • What is your management philosophy?
  • What is the role of data and metrics in managing a team like ours?
  • What role does the manager play in making technical decisions?
  • What is an example of a change you have made in the team that improved the team?
  • What would be the most important problem you would want me to solve if I joined your team?
  • What opportunities for growth will your team provide?
  • What would I work on if I joined this team and who would I work most closely with?

Leadership

These questions are intended for senior level management, such as CEO, CTO, VPs. Candidates who interview with startups usually get to speak with senior level management.

  • How are you funded?
  • Are you profitable? If no, what's your plan for becoming profitable?
  • What assurance do you have that this company will be successful?
  • Tell me about your reporting structure.
  • How does the company decide on what to work on next?

HR

  • How do you see this position evolving in the next three years?
  • Who is your ideal candidate and how can I make myself more like them?
  • What concerns/reservations do you have about me for this position?
  • What can I help to clarify that would make hiring me an easy decision?
  • How does the management team deal with mistakes?
  • If you could hire anyone to join your team, who would that be and why?
  • How long does the average engineer stay at the company?
  • Why have the last few people left?
  • Have you ever thought about leaving? If you were to leave, where would you go?

Once You've Got The Job

Congratulations!

Keep learning.

You're never really done.

*****************************************************************************************************
*****************************************************************************************************

Everything below this point is optional.
By studying these, you'll get greater exposure to more CS concepts, and will be better prepared for
any software engineering job. You'll be a much more well-rounded software engineer.

*****************************************************************************************************
*****************************************************************************************************

Additional Books

Additional Books

Additional Learning

Additional Learning

These topics will likely not come up in an interview, but I added them to help you become a well-rounded software engineer, and to be aware of certain technologies and algorithms, so you'll have a bigger toolbox.

Additional Detail on Some Subjects

Additional Detail on Some Subjects 
I added these to reinforce some ideas already presented above, but didn't want to include them
above because it's just too much. It's easy to overdo it on a subject.
You want to get hired in this century, right?

Video Series

Sit back and enjoy. "Netflix and skill" :P

Video Series

Computer Science Courses

Computer Science Courses

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CC-BY-SA-4.0

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