Cracking the Coding and PM Interviews

Cracking the Coding
(& PM) Interview
Advice and Strategies for Software Engineering
and Product Management Interviews
Gayle Laakmann McDowell
Founder / CEO, CareerCup.com
Author of Cracking the Coding Interview,
Cracking the PM Interview, & The Google Resume
McDowell | CareerCup.com
July 2013

Technical Skills
Behavioral
Applying

My Background
• Software Engineer @ Google, Microsoft & Apple
– 3 Years on Google Hiring Committee
– Interviewed 150+ candidates

• Founder of CareerCup.com
• Author
– Cracking the Coding Interview
– The Google Resume
– Cracking the PM Interview [Product Management]

Process

• Interview coach for acquisitions & acquihires


Technical Skills
Process

Applying

Behavioral

everyone

programmer
s

Technical Skills

Most Common CS Jobs
Big Company

Behavioral

PM

Dev

SDET

Startup

Research

Start Your
Own

Dev

Research

DO ALL
THE
THINGS

Senior & Up

Process

Applying

Junior

Sophomore

Freshman


Technical Skills
Behavioral

Product Manager (“PM”)
==
“Associate Product Manager”
(Google, Yahoo, Facebook, etc.)
==
“Program Manager”
(Microsoft)

Process

Applying

What is a Product Manager?


Technical Skills
Behavioral

• Manage the PRODUCT, not the PEOPLE
• “Build a great product for the users”
– Who are the users?
– What are the features?
– When will we launch?
– How do we launch?
– etc

Process

Applying

What is a Product Manager?


Technical Skills
Behavioral

Programmer
==
Software Engineer
==
Software Developer (Dev)
==
Software Design Engineer (SDE)
(Microsoft)

Process

Applying

What is a Programmer?


Technical Skills
Behavioral

• Write code (duh)
• Architect systems
• Plus sometimes:
– Write specs
– Talk to users
– Figure out feature set
– Etc

Process

Applying

What is a Programmer?


Technical Skills
Behavioral
Applying
Process

What is an SDET?
Software Test Engineer (SET)
(Google)
==
Software Design Engineer in Test
(SDET)
(Microsoft)
!=
Quality Assurance (QA)

• Figure out what needs to be tested and
how
• Write code to automate testing

Technical Skills
Process

Applying

Behavioral

What is an SDET?


Technical Skills

TODAY
– Experience
– Resumes
– Interviews
– Offers

Process

Applying

Behavioral

• Software Developer + PM


• 5 - 10 min – Qs about resume
• 40 min – technical Qs
– Coding and algorithms

• 5 – 10 min – let you ask Qs, general
wrap up, etc

Technical Skills
Process

Applying

Behavioral

What to Expect


Technical Skills

Big Company Evaluation (Devs)

Coding
Skills

Intelligence

Process

Applying

Behavioral

Experience
Personality


Testing
aptitude, not
knowledge

Technical Skills
Behavioral
Applying
Process

Start-Ups
• Coding + Intelligence
• “Hit the ground running”
– Do you know “their” technologies?

• Entrepreneurial
– Have you started things?
– How much direction do you need?
but…
• Personality
it varies!
– Will you fit with the team?

•
•
•
•
•

Communication Skills
User-Focused Thinking
Passion for Technology
Analytical Skills
Technical Skills (position dependent)

Process

Applying

Behavioral

Technical Skills

PM Roles


Technical Skills
Behavioral
Applying
Process

How You Are Judged
How did you do RELATIVE
to other candidates on
the SAME question?
It’s not about how
quickly you solved
the problem…
… it’s about how quickly
you solved it relative to
other candidates.

Resumes & Application Process


Technical Skills

How to Get an Interview
– Education
– Work Experience
– Projects
– Github / Online Profile

• Make a kick-ass resume

Process

Applying

Behavioral

• Your “Pedigree”


Technical Skills

PROJECTS???

Process

Applying

Behavioral

Did I mention…


Technical Skills

How We Review Resumes

3.

Applying

Behavioral

1.
2.

Reject

4.
Process

Pull resume out of giant stack
Spot-check: company names,
positions, projects, schools.
Skim bullets to see if you’ve
written real code.
Interview

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

“Glanced
at,” not read.
15 – 30
seconds

How CS Resume
Should Look
One Page Only!
Unless > 10 years exp.
A Real Resume Format
with organized columns
Short (1 – 2 line bullets)
Focus on Accomplishments
not responsibilities
GPA if at least 3.0
max (in-major, overall)

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

Observe: No Objective!
Objectives / summaries are
almost always useless.

Technical Skills

Talking to Recruiters
– What you’ve done (mobile app? Show it!)
– What you’re excited about

• Have a “pitch” ready
• Weird is okay
– (arrogant is not)

Process

Applying

Behavioral

• Show:


Soft Questions


Technical Skills
Behavioral

• Answer the question.
• Deliver a good answer.
• Communicate well.
– Nugget First
– S.A.R.: Situation, Action, Result

Process

Applying

Goals of Your Answer


Technical Skills

Preparing for Behavioral Qs
• Create Preparation Grid for Projects

Behavioral

OS Project

Amazon Intern.

Enjoyed
Hated

Applying

Most Challenging
Hardest Bug

Process

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

Technical Skills

Structure 1: Nugget First

Behavioral

• Lead with your “thesis” / nugget
– Grabs the listener’s attention
– Gives them context for where you’re going.

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

Process

Applying

Q: What accomplishment are you
most proud of?


Technical Skills

Structure 2: S.A.R.
What was the issue?

A ction

What did you do about it?

R esult

What was the impact?

Process

Applying

Behavioral

S ituation


Technical Skills

Good Questions for Interviewer

Behavioral

• Qs you want to get answered
– How decisions get made
– Interaction betw devs, PMs, testers

• Qs that show interest / passion
• Qs that show knowledge / aptitude
– How did you solve problem with ___?
Don’t worry too much
about this stuff

Process

Applying

– What’s the architecture like?


Technical Skills
Interview Prep


Technical Skills

How to study
• Study the basics

Behavioral

• Practice solving questions

Applying

– Complex algorithms generally unnecessary.

• Push yourself!
• Write code on paper

Process

– Don’t memorize!
– See: CtCI & CareerCup.com


Technical Skills
Behavioral

Data Structures
• How to implement
• When to use (pros / cons)
Queues

Trees

Tries

Graphs

Vectors

Applying

Stacks

Heaps

Hashtables

Process

Linked Lists


Technical Skills
Behavioral

• Implementation
• Space vs. Time
Complexity

Quick Sort

Merge Sort

Tree Insert / Find

Binary Search

Breadth-First
Search

Depth-First
Search

Process

Applying

Algorithms


Technical Skills

Concepts

Behavioral

• Not just a concept – know how to code!

Big-O
Time / Space

Memory
Management

Recursion

Probability +
Combinatorics

Bit Manipulation

Process

Applying

Threading


Technical Skills
Behavioral

• Necessary for “elite” tech companies
– Not necessarily otherwise (check interview
questions)

• MIT Open Courseware
– Freshman / sophomore level DS & Algo
courses

• Books
– CLRS (Algorithms)

• Online tutorials
• Practice implementing and using

Process

Applying

How to Learn CS Fundamentals?


Technical Skills
Mastering the Interview


Technical Skills
Behavioral

1. Product Design Questions
2. Estimation Questions
3. Software Engineering Questions
–
–
–
–

Coding & Algorithms
Object Oriented Design
Scalability
Factual / Trivia / Language-Based

Process

Applying

Types of “Serious” Questions


Technical Skills
Behavioral
Applying
Process

Product Design Questions
How would you design an
calculator for the blind?

Design an elevator for a building.

Pick a Google product.
How would you improve it?

Technical Skills
Behavioral
Applying
Process

Product Design Questions: Why?
•
•
•
•

Communication & Structured Thinking
Ability to understand the user
Creativity
Business instincts / skills

Technical Skills
Behavioral
Applying
Process

Product Design Qs: Approach
1.
2.
3.
4.

Ask questions to resolve ambiguity
Understand the user
Structure the problem
Solve piece by piece

Technical Skills
Behavioral
Applying
Process

Product Design Qs: Example
How would you design a calculator for the blind?

Step 1: Ask Questions
• Adults? Children? Professionals?
• Where are they using it?
– School, work, etc.

Technical Skills
Behavioral
Applying
Process


Step 2: Understand the User
• What’s important to a blind child?
– Keeping up with the rest of the class
– Not feeling “different”
– Efficient input / output

• What about teachers, parents,
classmates, etc.?

Technical Skills
Behavioral


Step 3: Structure
• Find a structure
– Otherwise, you’re just blabbering

Process

Applying

• One approach:
1.
2.
3.
4.

Make list of functions necessary
Discuss how to do input / output
Usability for non-blind
Summary

Technical Skills
Behavioral
Applying
Process


Step 4: Solve!

Technical Skills
Behavioral
Applying
Process

Estimation Questions
How many tennis balls
can fit in an SUV?
How much money does Gmail make
from ads every year?
How much do New Yorkers
spend on electricity each year?

Technical Skills

Estimation Qs: Why?

Process

Applying

Behavioral

• Problem Solving
• Basic Quantitative Skills

Technical Skills

Estimation Qs: How to Approach
1. Ask questions to resolve ambiguity

Applying

Behavioral

– Don’t make assumptions (yet)

2. Outline / Structure Your Approach
3. Break down the components
– Assume numbers when necessary
– State assumptions explicitly
– Round numbers to make your math easier

4. Sanity Check

Process

– Do your numbers make sense?

Technical Skills
Behavioral
Applying
Process

Estimation Qs: Example
How much money does Gmail make from ads every year?

Step 1: Ambiguous Information
• Profit or revenue?
• Past year? Or average over history?
• Gmail only? Or include Google Apps?

Technical Skills


Process

Applying

Behavioral

Step 2: Outline Your Approach
(# of users)
x
(# clicks / year)
x
( $ / click )

Technical Skills


Process

Applying

Behavioral

Step 3: Break down components
Estimate # of Gmail users in the US

1. Assume 300 million people in the US.
–
–

Exclude 0 - 12 years old and 65 - 75 years old
 ~ 200 million

2. Assume 80% of people use email
3. 80% of those have non-work account
… and so on …

Technical Skills
Behavioral
Applying
Process


Step 4: Validate Numbers
• Could revenue be $5 billion?
• No, because…
– Google’s annual revenue is ~$40 billion
– $16 / US citizen (not just Gmail users)

•
•
•
•

Knowledge Questions
Coding & Algorithms
Scalability

Product Design

Estimation

Technical

CS Questions


Technical

Knowledge & Trivia Questions
• Not key focus at “elite” tech companies.

Estimation

– If asked, tends to focus more on DS
knowledge than language knowledge

• If you don’t know, try to deduce the
answer

Product Design

– How would language designer do it? etc


Technical
Estimation
Product Design

Coding & Algorithm Questions
1. Understand the question
– Clarify, remember key details, etc.
2. Draw an example
–

“Sufficiently interesting”

3. Talk out loud
4. Analyze
– Does it work? What’s the big O time / space?
– Do YOU understand it?
If you’ve heard a
5. Code (SLOWLY)
question before,
6. Test + fix (CAREFULLY)
admit it.

Technical
Estimation

What does a “good coder” do?
• Be methodical. Don’t try to rush.
• Don’t code if you don’t understand
• Reasonably Bug Free
–
–

Thorough testing (and careful fixing)
Check for error conditions

Product Design

• Clean coding
–
–
–

Use other functions
Good use of data structures (define own if useful)
Concise and readable

Product Design

Estimation

Technical

Whiteboard Coding Tips
Code in the FAR top left corner
Write small & straight
Pseudocode if you’d like
Use arrows to insert new code snippets
Use “good” variable names, then
abbreviate
• “Breadth-First” Coding
•
•
•
•
•


Technical

“Breadth-First” Coding
• Divide problems into sub-components
• Ex: Ransom Note
– Write as one big function?
– OR… modularize!

Product Design

Estimation

– Modularize & Structure


Technical
Product Design

Estimation

Ex: Ransom Note:
“Depth-First” Coding


Technical
Product Design

Estimation

Ex: Ransom Note:
“Breadth-First” Coding


Technical
Estimation
Product Design

“Breath-First” Coding
•

“Depth-First” Coding (One big function)
– Messy
– Time consuming
– Poor coding style

•

“Breadth-First” Coding (Modularized)
–
–
–
–
–

“Finishes” algorithm immediately
Often allows you to skip details
Easier to test & fix issues
Demonstrates good coding style
Keeps YOU organized

Technical
Estimation

Common Mistakes
•
•

Ignoring information given
Not using examples
– To design algorithms
– While writing code

•

“Pushing through” code when confused

Product Design

– Incoherent thoughts -> incoherent code

•
•

Diving into code too quickly
The details:
– Off-by-one, < vs <=, division (and any math)

Technical

Types of Interview Questions

System Design

“Reverse a Linked
List”

“Design a Parking
Lot”

“Design a
Web Crawler”

Product Design

Estimation

Coding & Algorithms


Technical

Types of Interview Questions
Coding & Algorithms


Estimation

Pattern Matching
Simplify & Generalize

Product Design

Base Case & Build
Data Structure
Brainstorm


System Design

Technical

Algorithm Qs: Pattern Matching
Coding & Algorithms

Estimation

Pattern Matching

Product Design

Base Case & Build
Data Structure
Brainstorm


System Design

Q: Write code to reverse the order of words
in a sentence.
“dogs are cute”
“cute are dogs”
Similar to: reverse characters in a string.
“dogs are cute”
“etuc era sgod”
A: Reverse full string, then reverse each
word.

Technical

Algorithm Qs: Simplify & Generalize
Coding & Algorithms

Estimation

Pattern Matching

Product Design

Base Case & Build
Data Structure
Brainstorm


System Design

Q: Design algorithm to figure out if you can
build a ransom note (array of strings) from a
magazine (array of strings).
Simplify: what if we used characters instead
of strings?
 Build array of character frequencies.
Generalize: how we can extend answer to
words?
A: Build hashtable from word to frequency.

Technical

Algorithm Qs: Base Case & Build
Coding & Algorithms

Estimation

Pattern Matching

Product Design

Base Case & Build
Data Structure
Brainstorm


System Design

Q: Design algorithm to print subsets of set.
{a, b, c}
 {}, {a}, {b}, {c}, {a, b},
{a, c}, {b, c}, {a, b, c}
S({})
S({a})
S({a, b})
S({a, b, c})

 {}
 {}, {a}
 {}, {a}, {b}, {a, b}
?

A: Build S(n) by cloning S(n-1) and adding n
to the cloned sets.

Technical

Algorithm Qs: Data Structure Brainstorm
Coding & Algorithms

Estimation

Pattern Matching

Product Design

Base Case & Build
Data Structure
Brainstorm


System Design

Q: There are 10^10 possible phone #s.
Explain how you could efficiently implement
assignSpecificNum(num) and
assignAnyAvailableNum().
Array (sorted)? Too slow to remove num.
Linked list? Too slow to find specific num.
Hash table? Can’t iterate through free nums.
Tree? Ah-ha!
A: Store free #s in BST. Remove when taken.

Technical

How To Solve Algorithm Questions
Coding & Algorithms

Estimation

Pattern Matching

Product Design

Base Case & Build
Data Structure
Brainstorm


System Design

Compare to similar problems.
Solve first for a simplified / tweaked problem.

Solve for n = 1, and build solution for n = 2.
Try to apply data structure to solve problem.


Technical


Estimation

Coding & Algorithms


System Design

Handle Ambiguity
What about the question is ambiguous?
Design the Core Objects
What are the main objects in the system?

Product Design

Analyze Relationships
How are the objects related to each other?
Investigate Actions
What are the main operations?

Technical


Product Design

Estimation

Coding & Algorithms


System Design

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

How would you
design the data
structures and
objects for a
restaurant?

Design the Core Objects
Guest, Party, Table, Server, Host, …
Analyze Relationships
Server and Host are both Employees…

Investigate Actions
A Party is seated at a Table by a Host…

Technical

System Design

Estimation

Coding & Algorithms


System Design

Handle Ambiguity
What about the question is ambiguous?
Make Believe
Pretend there wasn’t so much data & solve

Product Design

Get Real
Go back to the real problem. What breaks?
Solve Problems
Solve the issues you just found.

Technical

System Design

Product Design

Estimation

Coding & Algorithms


System Design

Handle Ambiguity
Do the words need to be in a specific
order?

Given millions of
documents, find
all documents
which contain a
list of words.

Make Believe
Assume everything can fit on one machine.
Get Real
Must split up data across machines.

Solve Problems
Divide hash table by file or by keyword?

Technical

Whew! All Done!
Coding & Algorithms


System Design

Estimation

Pattern Matching

<Gulp> This is a lot of
stuff. Do I need to get
everything right?

Product Design

Base Case & Build
Data Structure
Brainstorm


Technical Skills
Behavioral
Applying
Process

Evaluation is RELATIVE,
not absolute.

It’s not about how
quickly you solved
the problem…

<Gulp> This is a lot of
stuff. Do I need to get
everything right?
</Gulp>

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

Behavioral

Technical Skills

Everyone makes mistakes.
Everyone!

Process

Applying

So RELAX!
Interviews are supposed to be hard!


Technical Skills

After Your Interview
• Follow-up with your recruiter

Applying

Behavioral

– No response != rejection

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

• Lots of randomness.

Process

– So if you fail, get up and try again.

Process

Applying

Behavioral

Technical Skills

Negotiation


Technical Skills
Behavioral
Applying

But I hate negotiating!
• Welcome to the club!
• You ARE in demand.
• Your offer will not be revoked.

Is this conversation SO terrible that
you’re willing to give up $1000+**?

Process

** and likely more


Technical Skills

Negotiation

Process

Applying

Behavioral

• Most->least negotiable (generally)
1.
2.
3.
4.

Signing bonus/relocation
Stock
Salary
Other benefits

• Easier if you have another offer
• Counter-offer
• What matters to you?

Technical Skills
Behavioral
Applying

Closing Advice
•
•
•
•
•

Do projects
Study for your interviews
Chase interviews
… but don’t chase money
If possible, go to an “elite” tech company
– (But don’t stay too long if that’s not what you
want!)

• Check-in on your career.

Process

– Is this what you want to do with your life?

CareerCup.com
• Interview Videos
• Resume Review
• Mock Interviews

Behavioral

Technical Skills

Other Resources

Process

Applying

Or, follow me online at…
• twitter.com/gayle
• facebook.com/gayle
• technologywoman.com
• gayle@careercup.com
• quora.com


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