Gayle McDowell: Cracking the coding interview

Cracking the Coding Interview
Advice and Strategies for
Software Engineering Interviews
Gayle Laakmann McDowell
Founder / CEO, CareerCup.com
Author of The Google Resume and Cracking the Coding Interview

McDowell | NIT Trichy | Feb 2012
CareerCup.com

Technical Skills
My Background
• Software Engineer @ GOOG, MS & Apple
– 3 Years on Google Hiring Committee
Behavioral

– Interviewed 150+ candidates
• Founder of CareerCup.com
• Author
Applying

– Cracking the Coding Interview
– The Google Resume
Process

McDowell | CareerCup.com

Technical Skills
Slides Posted Online
posted at:
www.technologywoman.com
Behavioral

Click “Speaking Engagements”
Applying
Process


Technical Skills
Process Applying
Evaluation Experience
Structure Resume
Behavioral

Soft Skills Tech Skills
Applying

Preparation Preparation
Interview Interview
Process


Interview Process


Technical Skills Big Company Evaluation (Coding)
Experience
Personality
Behavioral

Intelligence
Coding
Skills
Applying

Testing
aptitude, not
knowledge
Process


Technical Skills
How You Are Judged
How did you do RELATIVE
to other candidates on
the SAME question?
Behavioral

It’s not about how
quickly you solved
Applying

the problem…
… it’s about how quickly
you solved it relative to
Process

other candidates.

Resumes & Application Process


Technical Skills
Indians are at a disadvantage
• Far away
– Fewer recruiting opportunities
• Unfamiliar
Behavioral

– Recruiters may not understand your
school, GPA, etc
• Language barrier / Cultural differences
Applying

– Accents, grammar, accidental sexism
• Different / less experience
– More emphasis in US on projects
Process

Technical Skills
So what to do?
• Get equivalent experience
• Translate GPA & other items
Behavioral

• Use good grammar & punctuation
– On resumes, cover letters, etc
– No abbreviations, no sloppiness
Applying

• Be careful about your assumptions
– Sexism is not acceptable in the U.S. Ever.
Process

Technical Skills
Cheat Sheet for Indians
(Grammar / Writing)
• Space after comma & period. Never before.
– WRONG: “Hello .I am Gayle .”
– RIGHT: “Hello. I am Gayle.”
• Questions need a question mark
Behavioral

– WRONG: “Do you have one.”
– RIGHT: “Do you have one?”
• No abbreviations
– WRONG: “Ny1 dr?”
Applying

– RIGHT: “Is anyone there?”
• Commands are rude (use a question)
– WRONG: “Send it to me.”
– RIGHT: “Would you mind sending it to me?”
Process

Technical Skills
(Gender / Sexism)
• Mr. LastName / Ms. LastName
– WRONG: Ms. Gayle
– RIGHT: Ms. McDowell
Behavioral

– But “Dear Gayle” is perfectly okay in U.S.
• “Guy” / “Guys” is not unisex* in the U.S.
– WRONG: “I need to hire a really smart CS guy.”
– *Except: “you guys” and “hey guys”
• Don’t assume that people are male / female
Applying

– (Just don’t use Mr. / Ms. in emails!)
• It is EXTREMELY offensive to comment on
someone’s looks
– But a great way to get fired / rejected
Process

Technical Skills
(Getting Experience)
• Build something!
Don’t waste your summers!
Behavioral

• Make a kick-ass resume
It’s really not that hard.
Applying
Process


Technical Skills How We Review Resumes (U.S.)
1. Pull resume out of giant stack
2. Spot-check: company names, “Glanced
at,” not read.
positions, projects, schools.
Behavioral

15 – 30
3. Skim bullets to see if you’ve seconds

written real code.
Applying

Reject Interview

4. Go to next resume & whine about
how many more you have left.
Process


How CS Resume
Should Look (U.S.) Observe: No Objective!
Objectives / summaries
One Page Only! are almost always useless.
Unless > 10 years exp.

A Real Resume Format
with organized columns

Short (1 – 2 line bullets)

Focus on Accomplishments
not responsibilities
GPA - Translated
We don’t understand
“first class”

3 – 4 Projects
Courses & independent
Finished or unfinished
List of Technical Skills
Short! Cut the “fluff.”

Behavioral Questions


Technical Skills
Communication Tips
• Goals:
– Answer the question.
Behavioral

– Deliver a *good* answer.
– Communicate well.
• Strategies:
Applying

– Nugget First
– S.A.R.: Situation, Action, Result
Process


Technical Skills
Preparing for Behavioral Qs
• Create Preparation Grid for Projects
OS Project Amazon Intern.
Behavioral

Enjoyed

Hated

Most Challenging
Applying

Hardest Bug

+ Behavioral Grid [for PM & less tech. roles]
Process


Technical Skills
Structure 1: Nugget First
• Lead with your “thesis” / nugget
– Grabs the listener’s attention
Behavioral

– Gives them context for where you’re going.
Q: What accomplishment are you
most proud of?
Applying

A: I’m most proud of the way I
re-architected the …
Process


Technical Skills
Structure 2: S.A.R.

S ituation What was the issue?
Behavioral

A ction What did you do about it?

R esult What was the impact?
Applying
Process


Technical Skills
Interview Prep


Technical Skills
How to study
• Study the basics
– Complex algorithms generally unnecessary.
Behavioral

• Practice solving questions
– Don’t memorize!
– See: CtCI & CareerCup.com
Applying

• Push yourself!
• Write code on paper
Process


Technical Skills
Data Structures
• How to implement
• When to use (pros / cons)
Behavioral

Linked Lists Stacks Queues

Trees Tries Graphs
Applying

Vectors Heaps Hashtables
Process


Technical Skills
Algorithms
• Implementation
• Space vs. Time Quick Sort Merge Sort
Complexity
Behavioral

Tree Insert / Find Binary Search
Applying

Breadth-First Depth-First
Search Search
Process


Technical Skills
Concepts
• Not just a concept – know how to code!
Behavioral

System Design & Memory
Threading
Scalability Management
Applying

Probability +
Recursion Bit Manipulation
Combinatorics
Process


Technical Skills
Mastering the Interview


Technical Skills
Technical Questions
1. Ask Questions!
– Questions are more ambiguous than they appear
2. Talk out loud
Behavioral

– 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
Applying

– It’s not a race
5. Test your code
– And make CAREFUL fixes.
Process


Technical Skills
What does a “good coder” do?
• Be methodical. Don’t try to rush.
• Reasonably Bug Free
Behavioral

– Thorough testing (and careful fixing)
– Check for error conditions
• Clean coding
– Use other functions
Applying

– Good use of data structures (define own if useful)
– Concise and readable
Process


Technical Skills Types of Interview Questions
Coding & Algorithms Object Oriented Design System Design

“Reverse a Linked “Design a Parking “Design a
Behavioral

List” Lot” Web Crawler”
Applying
Process


Technical Skills Types of Interview Questions


Pattern Matching
Behavioral

Simplify & Generalize

Base Case & Build
Applying

Data Structure
Brainstorm
Process


Technical Skills Algorithm Qs: Pattern Matching


Pattern Matching
Q: Write code to reverse the order of words
Behavioral

in a sentence.
Simplify & Generalize “dogs are cute”
“cute are dogs”

Base Case & Build Similar to: reverse characters in a string.
Applying

“dogs are cute”
Data Structure “etuc era sgod”
Brainstorm
A: Reverse full string, then reverse each
word.
Process


Technical Skills Algorithm Qs: Simplify & Generalize


Pattern Matching
Q: Design algorithm to figure out if you can
Behavioral

build a ransom note (array of strings) from a
Simplify & Generalize magazine (array of strings).

Simplify: what if we used characters instead
Base Case & Build of strings?
Applying

 Build array of character frequencies.
Data Structure
Brainstorm Generalize: how we can extend answer to
words?
Process

A: Build hashtable from word to frequency.

Technical Skills Algorithm Qs: Base Case & Build


Pattern Matching Q: Design algorithm to print subsets of set.
Behavioral

{a, b, c}  {}, {a}, {b}, {c}, {a, b},
Simplify & Generalize {a, c}, {b, c}, {a, b, c}

S({})  {}
Base Case & Build S({a})  {}, {a}
Applying

S({a, b})  {}, {a}, {b}, {a, b}
Data Structure S({a, b, c}) ?
Brainstorm
A: Build S(n) by cloning S(n-1) and adding n
to the cloned sets.
Process


Technical Skills Algorithm Qs: Data Structure Brainstorm


Pattern Matching Q: There are 10^10 possible phone #s.
Behavioral

Explain how you could efficiently implement
Simplify & Generalize assignSpecificNum(num) and
assignAnyAvailableNum().

Base Case & Build Array (sorted)? Too slow to remove num.
Applying

Linked list? Too slow to find specific num.
Data Structure Hash table? Can’t iterate through free nums.
Brainstorm Tree? Ah-ha!

A: Store free #s in BST. Remove when taken.
Process


Technical Skills How To Solve Algorithm Questions


Pattern Matching Compare to similar problems.
Behavioral

Simplify & Generalize Solve first for a simplified / tweaked problem.

Base Case & Build
Solve for n = 1, and build solution for n = 2.
Applying

Data Structure
Brainstorm Try to apply data structure to solve problem.
Process


Technical Skills Object Oriented Design


Handle Ambiguity
Behavioral

What about the question is ambiguous?

Design the Core Objects
What are the main objects in the system?
Applying

Analyze Relationships
How are the objects related to each other?

Investigate Actions
What are the main operations?
Process


Technical Skills Object Oriented Design


Handle Ambiguity
Behavioral

Is it a single restaurant, or part of a chain?

How would you Design the Core Objects
design the data Guest, Party, Table, Server, Host, …
structures and
Applying

objects for a Analyze Relationships
Server and Host are both Employees…
restaurant?
Investigate Actions
A Party is seated at a Table by a Host…
Process


Technical Skills System Design


Handle Ambiguity
Behavioral

What about the question is ambiguous?

Make Believe
Pretend there wasn’t so much data & solve
Applying

Get Real
Go back to the real problem. What breaks?

Solve Problems
Solve the issues you just found.
Process


Technical Skills System Design


Handle Ambiguity
Behavioral

Do the words need to be in a specific
order?
Given millions of
documents, find Make Believe
Assume everything can fit on one machine.
all documents
Applying

which contain a Get Real
list of words. Must split up data across machines.

Solve Problems
Process

Divide hash table by file or by keyword?

Technical Skills Whew! All Done!


Pattern Matching
Behavioral

<Gulp> This is a lot of
Simplify & Generalize stuff. Do I need to get
everything right?
Base Case & Build
Applying

Data Structure
Brainstorm
Process


Technical Skills
Evaluation is RELATIVE,
not absolute.
Behavioral

<Gulp> This is a lot of
stuff. Do I need to get
It’s not about how everything right?
quickly you solved
the problem…
Applying

</Gulp>

… it’s about how quickly
you solved it relative to
other candidates.
Process


Technical Skills

So RELAX!
Behavioral

Interviews are supposed to be hard!

Everyone makes mistakes.
Applying

Everyone!
Process


Final Thoughts


Technical Skills
After Your Interview
• Follow-up with your recruiter
– No response != rejection
Behavioral

• You have no idea how well/poorly you
did.
– Seriously. I know you think you do. But you
don’t.
Applying

• Lots of randomness.
– So if you fail, get up and try again.
Process


Technical Skills
Other Resources
Sold Today CareerCup.com
• Interview Videos
Signed (just ask!) • iPhone App
• Resume Review
• Mock Interviews
Behavioral

today Or, stalk me online at…
Rs. • twitter.com/gayle
400 • facebook.com/gayle
• technologywoman.com
Applying

• gayle@careercup.com

5 stars!
Process


Gayle McDowell: Cracking the coding interview

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