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Coding Interview University

I originally created this as a short to-do list of study topics for becoming a software engineer, but it grew to the large list you see today. After going through this study plan, I got hired as a Software Development Engineer at Amazon! You probably won't have to study as much as I did. Anyway, everything you need is here.

I studied about 8-12 hours a day, for several months. This is my story: Why I studied full-time for 8 months for a Google interview

Please Note: You won't need to study as much as I did. I wasted a lot of time on things I didn't need to know. More info about that below. I'll help you get there without wasting your precious time.

The items listed here will prepare you well for a technical interview at just about any software company, including the giants: Amazon, Facebook, Google, and Microsoft.

Best of luck to you!

Translations:
Translations in progress:

Become a sponsor and support Coding Interview University!

Special thanks to:

OSS Capital
Founded in 2018, OSS Capital is the first and only venture capital platform focused
exclusively on supporting early-stage COSS (commercial open source) startup founders.


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What is it?

Coding at the whiteboard - from HBO's Silicon Valley

This is my multi-month study plan for becoming a software engineer for a large company.

Required:

  • A little experience with coding (variables, loops, methods/functions, etc)
  • Patience
  • Time

Note this is a study plan for software engineering, not web development. Large software companies like Google, Amazon, Facebook and Microsoft view software engineering as different from web development. For example, Amazon has Frontend Engineers (FEE) and Software Development Engineers (SDE). These are 2 separate roles and the interviews for them will not be the same, as each has its own competencies. These companies require computer science knowledge for software development/engineering roles.

Table of Contents

The Study Plan

Topics of Study

Getting the Job

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

Optional Extra Topics & Resources

Why use it?

If you want to work as a software engineer for a large company, these are the things you have to know.

If you missed out on getting a degree in computer science, like I did, this will catch you up and save four years of your life.

When I started this project, I didn't know a stack from a heap, didn't know Big-O anything, or anything about trees, or how to traverse a graph. If I had to code a sorting algorithm, I can tell ya it would have been terrible. Every data structure I had ever used was built into the language, and I didn't know how they worked under the hood at all. I 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 used a few multidimensional arrays in my life and thousands of associative arrays, but I 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

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 track 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

Fork the GitHub repo https://github.com/jwasham/coding-interview-university by clicking on the Fork button.

Clone to your local repo:

git clone [email protected]:<your_github_username>/coding-interview-university.git
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/main
git push --set-upstream origin progress
git push --force

More about GitHub-flavored markdown

Don't feel you aren't smart enough

A Note 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.

It would be great to replace the online course resources with free and always-available public sources, such as YouTube videos (preferably university lectures), so that you people can study these anytime, not just when a specific online course is in session.

Choose a Programming Language

You'll need to choose a programming language for the coding interviews you do, but you'll also need to find a language that you can use to study computer science concepts.

Preferably the language would be the same, so that you only need to be proficient in one.

For this Study Plan

When I did the study plan, I used 2 languages for most of it: C and Python

  • C: Very low level. Allows you to deal with pointers and memory allocation/deallocation, so you feel the data structures and algorithms in your bones. In higher level languages like Python or Java, these are hidden from you. In day to day work, that's terrific, but when you're learning how these low-level data structures are built, it's great to feel close to the metal.
    • C is everywhere. You'll see examples in books, lectures, videos, everywhere while you're studying.
    • The C Programming Language, Vol 2
      • This is a short book, but it will give you a great handle on the C language and if you practice it a little you'll quickly get proficient. Understanding C helps you understand how programs and memory work.
      • You don't need to go super deep in the book (or even finish it). Just get to where you're comfortable reading and writing in C.
      • Answers to questions in the book
  • Python: Modern and very expressive, I learned it because it's just super useful and also allows me to write less code in an interview.

This is my preference. You do what you like, of course.

You may not need it, but here are some sites for learning a new language:

For your Coding 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 could also use these, but read around first. There may be caveats:

  • JavaScript
  • Ruby

Here is an article I wrote about choosing a language for the interview: Pick One Language for the Coding Interview. This is the original article my post was based on: http://blog.codingforinterviews.com/best-programming-language-jobs/

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

Read more about choices:

See language-specific resources here

Books for Data Structures and Algorithms

This book will form your foundation for computer science.

Just choose one, in a language that you will be comfortable with. You'll be doing a lot of reading and coding.

C

Python

Java

Your choice:

C++

Your choice:

Interview Prep Books

You don't need to buy a bunch of these. Honestly "Cracking the Coding Interview" is probably enough, but I bought more to give myself more practice. But I always do too much.

I bought both of these. They gave me plenty of practice.

If you have tons of extra time:

Choose one:

Don't Make My Mistakes

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

Here are some mistakes I made so you'll have a better experience. And you'll save months of time.

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. I didn't need all of that knowledge.

Please, read 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 or tablet, wherever I am.

Make your own for free:

I DON'T RECOMMEND using my flashcards. There are too many and many of them are trivia that you don't need.

But if you don't want to listen to me, here you go:

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).

Some students have mentioned formatting issues with white space that can be fixed by doing the following: open deck, edit card, click cards, select the "styling" radio button, add the member "white-space: pre;" to the card class.

3. Do Coding Interview Questions While You're Learning

THIS IS VERY IMPORTANT.

Start doing coding interview questions while you're learning data structures and algorithms.

You need to apply what you're learning to solving problems, or you'll forget. I made this mistake.

Once you've learned a topic, and feel somewhat comfortable with it, for example, linked lists:

  1. Open one of the coding interview books (or coding problem websites, listed below)
  2. Do 2 or 3 questions regarding linked lists.
  3. Move on to the next learning topic.
  4. Later, go back and do another 2 or 3 linked list problems.
  5. Do this with each new topic you learn.

Keep doing problems while you're learning all this stuff, not after.

You're not being hired for knowledge, but how you apply the knowledge.

There are many resources for this, listed below. Keep going.

4. Focus

There are a lot of distractions that can take up valuable time. Focus and concentration are hard. Turn on some music without lyrics and you'll be able to focus pretty well.

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

The Daily Plan

This course goes over a lot of subjects. Each will probably take you a few days, or maybe even a week or more. It depends on your schedule.

Each day, take the next subject in the list, watch some videos about that subject, and then write an implementation of that data structure or algorithm in the language you chose for this course.

You can see my code here:

You don't need to memorize every algorithm. You just need to be able to understand it enough to be able to write your own implementation.

Coding Question Practice

Why is this here? I'm not ready to interview.

Then go back and read this.

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 (see Big-O below)
  • 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

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

If you don't have a whiteboard at home, 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 just for scale. If you use a pen, you'll wish you could erase. Gets messy quick. I use a pencil and eraser.

my sofa whiteboard

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

Coding Problems

Don't forget your key coding interview books here.

Solving Problems:

Coding Interview Question Videos:

Challenge sites:

Let's Get Started

Alright, enough talk, let's learn!

But don't forget to do coding problems from above while you learn!

Algorithmic complexity / Big-O / Asymptotic analysis

Well, that's about enough of that.

When you go through "Cracking the Coding Interview", there is a chapter on this, and at the end there is a quiz to see if you can identify the runtime complexity of different algorithms. It's a super review and test.

Data Structures

  • Arrays

    • About Arrays:
    • Implement a vector (mutable array with automatic resizing):
      • Practice coding using arrays and pointers, and pointer math to jump to an index instead of using indexing.
      • New raw data array with allocated memory
        • can allocate int array under the hood, just not use its features
        • start with 16, or if starting number is greater, use power of 2 - 16, 32, 64, 128
      • size() - number of items
      • capacity() - number of items it can hold
      • is_empty()
      • at(index) - returns item at given index, blows up if index out of bounds
      • push(item)
      • insert(index, item) - inserts item at index, shifts that index's value and trailing elements to the right
      • prepend(item) - can use insert above at index 0
      • pop() - remove from end, return value
      • delete(index) - delete item at index, shifting all trailing elements left
      • remove(item) - looks for value and removes index holding it (even if in multiple places)
      • find(item) - looks for value and returns first index with that value, -1 if not found
      • resize(new_capacity) // private function
        • when you reach capacity, resize to double the size
        • when popping an item, if size is 1/4 of capacity, resize to half
    • Time
      • O(1) to add/remove at end (amortized for allocations for more space), index, or update
      • O(n) to insert/remove elsewhere
    • Space
      • contiguous in memory, so proximity helps performance
      • space needed = (array capacity, which is >= n) * size of item, but even if 2n, still O(n)

  • Linked Lists

    • Description:
    • C Code (video) - not the whole video, just portions about Node struct and memory allocation
    • Linked List vs Arrays:
    • why you should avoid linked lists (video)
    • Gotcha: you need pointer to pointer knowledge: (for when you pass a pointer to a function that may change the address where that pointer points) This page is just to get a grasp on ptr to ptr. I don't recommend this list traversal style. Readability and maintainability suffer due to cleverness.
    • Implement (I did with tail pointer & without):
      • size() - returns number of data elements in list
      • empty() - bool returns true if empty
      • value_at(index) - returns the value of the nth item (starting at 0 for first)
      • push_front(value) - adds an item to the front of the list
      • pop_front() - remove front item and return its value
      • push_back(value) - adds an item at the end
      • pop_back() - removes end item and returns its value
      • front() - get value of front item
      • back() - get value of end item
      • insert(index, value) - insert value at index, so current item at that index is pointed to by new item at index
      • erase(index) - removes node at given index
      • value_n_from_end(n) - returns the value of the node at nth position from the end of the list
      • reverse() - reverses the list
      • remove_value(value) - removes the first item in the list with this value
    • Doubly-linked List

  • Stack

    • Stacks (video)
    • Will not implement. Implementing with array is trivial

  • Queue

    • Queue (video)
    • Circular buffer/FIFO
    • Implement using linked-list, with tail pointer:
      • enqueue(value) - adds value at position at tail
      • dequeue() - returns value and removes least recently added element (front)
      • empty()
    • Implement using fixed-sized array:
      • enqueue(value) - adds item at end of available storage
      • dequeue() - returns value and removes least recently added element
      • empty()
      • full()
    • Cost:
      • a bad implementation using linked list where you enqueue at head and dequeue at tail would be O(n) because you'd need the next to last element, causing a full traversal each dequeue
      • enqueue: O(1) (amortized, linked list and array [probing])
      • dequeue: O(1) (linked list and array)
      • empty: O(1) (linked list and array)

  • Hash table

More Knowledge

Trees

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

Even More Knowledge

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.

Update Your Resume

Find a Job

Interview Process & General Interview Prep

Mock Interviews:

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 at least one answer 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]?

  • If you find it hard to come up with good answers of these types of interview questions, here are some ideas:

Have questions for the interviewer

Some of mine (I already may know the answers, 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?
  • How is the work/life balance?

Once You've Got The Job

Congratulations!

Keep learning.

You're never really done.

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

Everything below this point is optional. It is NOT needed for an entry-level interview.
However, 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

These are here so you can dive into a topic you find interesting.
  • The Unix Programming Environment
    • An oldie but a goodie
  • The Linux Command Line: A Complete Introduction
    • A modern option
  • TCP/IP Illustrated Series
  • Head First Design Patterns
    • A gentle introduction to design patterns
  • Design Patterns: Elements of Reusable Object-Oriente​d Software
    • AKA the "Gang Of Four" book, or GOF
    • The canonical design patterns book
  • 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.
        • This book is better as an algorithm reference, and not something you read cover to cover.
    • Can rent it on Kindle
    • Answers:
    • Errata
  • 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
  • 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
  • Computer Architecture, Sixth Edition: A Quantitative Approach
    • For a richer, more up-to-date (2017), but longer treatment

System Design, Scalability, Data Handling

You can expect system design questions if you have 4+ years of experience.

Additional Learning

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

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.

Computer Science Courses

Algorithms implementation

Papers

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