Cracking the coding interview columbia - march 23 2011

CAREERCUP

Cracking the Technical InterviewGayle Laakmann

Founder / CEO, CareerCup.com

Cracking the Coding Interview

Process Applying Prep (Soft) Prep (Tech) Interview (Soft) Interview (Tech)


My Background• CS undergrad and masters degree from UPenn• Ex-Engineer at Google, Microsoft and Apple– plus Offers from Amazon, IBM and others– 3 Years on Google Hiring Committee– Interviewed 150+ candidates

• Founder of CareerCup.com• Author of Cracking the Coding Interview and

The Google Resume



Process

Evaluation

Structure

Applying

Experience

Resume

Soft Skills

Preparation

Interview

Tech Skills

Preparation

Interview

CAREERCUP

How are interviews structured?How are you evaluated?

PROCESS



Technical Interview Process• Initial Screen (Phone / Campus)• 4 - 5 on site interviews– 10 min General– 40 min Technical– 10 min Closing



Big Company Evaluation

SmartCoding

ExperiencePersonality

Testing aptitude, not

knowledge



What are red flags?• Arrogance• Communication Issues• Arguing (too much)• Dishonesty

and…No Red

Flags



Smaller Companies• Tend to look for broader skills• Care more about experience / personality• Might ask to see “portfolio”

but…It varies!

CAREERCUP

What do companies look for?

APPLYING



What can you do?• Get project experience!– Course work– Open source– Part-time job– Start a business!

• Know C++ or Java well• Good grades are nice – but not enough!

Skills PassionWork EthicCreativityInitiative

But unless you show this on your resume, it really doesn’t do you much good.

So what should a resume look like?



Resumes – The Most Important Thing• Glanced at, not read– You have 15 – 30 seconds to make the best

impression possible.

• Show That You “Get Things Done”



Resumes: Structure1. One Page2. Short Bullets: 1 – 2 lines– “So short that you can’t NOT but read it”

3. Nice Resume Format– Use tables, not spaces.– Use a REAL resume format.



Resumes: Content1. Accomplishments, not responsibilities– Quantify!

2. Understandable, but specific– To be read by both recruiters and engineers

3. PROJECTS!– Anything (esp. coding) you did – for class or not



How do you make yourself look good?

INTERVIEW PREP – SOFT SKILLS



• Research the company / team– Prepare questions (around 10)

• Prepare for questions about yourself

But how?

Soft Skills Prep



• Create Preparation Grid for ProjectsOS Project Internship

Enjoyed

Hated

Most Challenging

Hardest Bug

+ (maybe) Behavioral Grid

Soft Prep – Yourself



How to handle “soft skills” questions

INTERVIEW – SOFT SKILLS



Communication Tips• Be specific – not arrogant

“Yeah, I did all the hard work for the team” “I implemented the file system, which was considered one of the hardest components.”

• Be concise and structured– Nugget First– S.A.R.: Situation, Action, Result



• Lead with your “thesis” / nugget– Nuggets grab the listener’s attention, and tell

them where you’re going

• Q: What accomplishment are you most proud of?

• A: The time that I convinced the engineering school to switch to paperless time logs.

Structure 1: Nugget First



ituationctionesult

Structure 2: S.A.R.

SAR

What did you do? What should I care?



How do you prep for coding questions?What do you prep?

INTERVIEW PREP – TECH SKILLS



• Write code on paper– Put away the compiler

• Study the basics: – CLR algorithms book is great –

but too complex for interviews• Look up sample interview questions– Focus on the topics you’re struggling with

How to study



• How to implement• When to use (pros / cons)

Data Structures

Linked Lists Stacks Queues

Trees Tries Graphs

Vectors Heaps HASHTABLES



• Implementation• Space vs Time Complexity

Algorithms

With eyes closed: With some thought:

Breadth-First Search Mergesort

Depth-First Search Quicksort

Tree Insert / Find Binary search



Concepts

Threading Locks + Mutexes

MemoryManagement

Recursion Probability + Combinatorics

Bit Manipulation

• Not just a concept – know how to code!



How do you tackle hard tech questions?

INTERVIEW – TECH SKILLS



Interview Coding



Mastering the Coding Questions1. Ask Questions!– Questions are more ambiguous than they appear

2. Talk out loud– Show us how you think

3. Think critically– Does your algorithm really work? What’s the space

and time complexity?4. Code slowly and methodically– It’s not a race

5. Test your code– You’re not done until they say you’re done!



What does a “good coder” do?• Be methodical, not speed• Reasonably Bug Free– Thorough testing (and careful fixing)– Check for error conditions

• Clean coding– Uses other functions– Good use of data structures (defines own if

useful)– Concise and readable



Solving Interview Problems



3 Main Question Types• Standard Coding and Algorithms– “Reverse a linked list”

• Object Oriented Design– “Design a parking lot”

• Scalability– “Design a program to crawl the web”



Algorithms

Question Type #1



How To Solve Algorithm Questions

• Pattern Matching– What problem is this similar to?

• Simplify / Generalize– What if the data was a different type?

• Base Case & Build– Can you do this just for element 1? 1 and 2? …

• Data Structure Brainstorm– Go through all data structures – can they help?

#1Standard Coding and Algorithms



Algorithm Generation• Pattern Matching

Write code to reverse the order of words in a sentence.Example:

input: “she ran to the store”output: “store the to ran she”




Algorithm Generation• Simplify / Generalize

Design an algorithm to figure out if you can build a ransom note (array of strings) from a magazine (array of strings).




Algorithm Generation• Base Case & Build

Design an algorithm to print all subsets of a set (e.g., the power set)Example:

input: {a, b, c}output: {{}, {a}, {b}, {c}, {a, b}, {a, c},

{b, c}, {a, b, c}}




Algorithm Generation• Data Structures Brainstorm

Design an algorithm to figure out if someone has won a game of tic-tac-toe. Make it as fast as possible.




Object Oriented Design

Question Type #2



Core objectswhat are the core objects?

Relationshipswhat is their relationship to each other?

Interactionshow do they interact?

Algorithmswhat are the tricky / interesting algorithms?

Object Oriented Design Steps (C.R.I.A.) #2Object Oriented

Design



OOD Example

Design the data structures for a restaurant

#2Object Oriented

Design



Core objectsrestaurant, host, employee, server, table

Relationshipseach party has many guests, server and host are a type of employee

InteractionsHOST assigns PARTY to TABLE

AlgorithmsHow is a free table selected?

Object Oriented Design Steps (C.R.I.A.) #2Object Oriented

Design



Scalability

Question Type #3



Simplifypretend there wasn’t a lot of data. How would you solve it?

Identify the problemswhat goes wrong when you have lots of data?

Fix the issuessolve the issues that come up

Iteratenew problems may have come up. How do you solve them?

Scalability Questions #3Scalability



RELAX!Interviews are

supposed to be hard!

Everyone makes mistakes. Everyone!



(eg, things that wouldn’t fit in elsewhere)

FINAL THOUGHTS



The Interview: Ending It• Smile, be positive• If you think you bombed, don’t worry• Follow up with your recruiters (sometimes

they forget)



My Red Flags: People who…… didn’t test their code… found mistakes and would make random fixes… messy code (lack of data structures /

redundant code)… didn’t consider the impact of their algorithms… were scared to try



• Books (sold today - $20)• Interview video• Mock Interviews• Resume Review

Other Resources

Slides posted at CareerCup.com/slides

Documents

Cracking the coding interview columbia - march 23 2011