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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

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:

Coding Interview University is supported by the community.

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.


What is it?

This is my multi-month study plan for going from web developer (self-taught, no CS degree) to software engineer for a large company.

Coding at the whiteboard - from HBO's Silicon Valley

This is meant for new software engineers or those switching from software/web development to software engineering (where computer science knowledge is required). If you have many years of experience and are claiming many years of software engineering experience, expect a harder interview.

If you have many years of software/web development experience, note that large software companies like Google, Amazon, Facebook and Microsoft view software engineering as different from software/web development, and they require computer science knowledge.

If you want to be a reliability engineer or operations engineer, study more from the optional list (networking, security).

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

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

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

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 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.

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:

Choose one:

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 through 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++

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

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

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.

Please, read so you won't make my mistakes:

Retaining Computer Science Knowledge.

A course recommended to me (haven't taken it): Learning how to Learn.

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. 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 comfortable with it, like linked lists, open one of the coding interview books and do a couple of questions regarding linked lists. Then move on to the next learning topic. Then later, go back and do another linked list problem, or recursion problem, or whatever. But keep doing problems while you're learning. You're not being hired for knowledge, but how you apply the knowledge. There are several books and sites I recommend. See here for more: Coding Question Practice.

4. 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.

5. 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

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 or Java))
  • 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

Algorithmic complexity / Big-O / Asymptotic analysis

Data Structures

  • Arrays

    • Implement an automatically resizing vector.
    • Description:
    • 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

System Design, Scalability, Data Handling

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

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

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. I use a pencil and eraser.

my sofa whiteboard

Supplemental:

Read and Do Programming Problems (in this order):

See Book List above

Coding exercises/challenges

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:

Language-learning sites, with challenges:

Challenge repos:

Mock Interviews:

Once you're closer to the interview

Best way to find perfect career opportunities for you

  • If you are trying to find new job opportunities, or if you are trying to find internships, if want to know about the salary of a job role in any companies or want to just know about the company reputation before applying to that company, here are the list of platforms which can help you find the above answers and more.
  • Best Websites for Careers & Jobs

Your Resume

  • See Resume prep items in Cracking The Coding Interview and back of Programming Interviews Exposed
  • Very Important thing to remember while creating your resume, if you applying for big companies is that make it ATS Compliant.
  • How to Create or Check if your Resume is ATS Compliant

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]?

  • If you find hard to come up with good answers of this type interview questions, you can refer below link for some answer templates and have some idea.

  • General Interview Questions and their Answers

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?
  • How is work/life balance?

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

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

  • UNIX and Linux System Administration Handbook, 5th Edition

  • 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

  • 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

  • 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

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

LICENSE

CC-BY-SA-4.0