Cracking the oding interview code chix - oct 2012

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

McDowell | CareerCup.com | Women Who Code
Aug 2012

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

– Interviewed 150+ candidates
• Founder of CareerCup.com
– 8000+ tech interview questions
Applying

• Author
– 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
“Elite” Tech Companies
Experience
Personality
Behavioral

Intelligence
Coding
Skills
Applying

Testing
aptitude, not
knowledge
Process


Technical Skills
Start-Ups
• Coding + Intelligence
• “Hit the ground running”
Behavioral

– Do you know “their” technologies?
• Entrepreneurial
– Have you started things?
Applying

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


Technical Skills
PM Roles
• Communication Skills
• User-Focused Thinking
Behavioral

• Passion for Technology
• Analytical Skills
• Technical Skills (position dependent)
Applying
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
How to Get an Interview
• Your “Pedigree”
– Education
Behavioral

– Work Experience
– Projects
– Github / Online Profile
• Make an awesome resume
Applying
Process


Technical Skills
How We Review Resumes
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 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 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.”

Technical Skills
Talking to Recruiters
• Show:
– What you’ve done (mobile app? Show it!)
Behavioral

– What you’re excited about
• Have a “pitch” ready
• Weird is okay
Applying

– (arrogant is not)
Process


Behavioral Questions


Technical Skills
Communication Goals
• Answer the question.
• Deliver a *good* answer.
Behavioral

• Communicate well.
Applying
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 How to Learn CS Fundamentals?
• Necessary for “elite” tech companies
– Not necessarily otherwise (check interview
questions)
Behavioral

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

– CLRS (Algorithms)
• Online tutorials
• Practice implementing and using
Process


Technical Skills
Mastering the Interview


Technical
Types of “Serious” Questions
1. Product Design Questions
2. Estimation Questions
3. Software Engineering Questions
Estimation

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


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

Design an elevator for a building.

Pick a Google product.
Product Design

How would you improve it?

Technical Product Design Questions: Why?
• Communication & Structured Thinking
• Ability to understand the user
• Creativity
Estimation

• Business instincts / skills
Product Design

Technical
Product Design Qs: Approach
1. Ask questions to resolve ambiguity
2. Understand the user
3. Structure the problem
Estimation

4. Solve piece by piece
Product Design

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

Step 1: Ask Questions
• Adults? Children? Professionals?
Estimation

• Where are they using it?
– School, work, etc.
Product Design

Technical

Step 2: Understand the User
• What’s important to a blind child?
Estimation

– Keeping up with the rest of the class
– Not feeling “different”
– Efficient input / output
• What about teachers, parents,
Product Design

classmates, etc.?

Technical

Step 3: Structure
• Find a structure
Estimation

– Otherwise, you’re just blabbering
• One approach:
1. Make list of functions necessary
2. Discuss how to do input / output
Product Design

3. Usability for non-blind
4. Summary

Technical

Step 4: Solve!
Estimation
Product Design

Technical
Estimation Questions
How many tennis balls
can fit in an SUV?
Estimation

How much money does Gmail make
from ads every year?

How much do New Yorkers
Product Design

spend on electricity each year?

Technical
Estimation Qs: Why?
• Problem Solving

• Basic Quantitative Skills
Estimation
Product Design

Technical Estimation Qs: How to Approach
1. Ask questions to resolve ambiguity
– Don’t make assumptions (yet)
2. Outline / Structure Your Approach
3. Break down the components
Estimation

– Assume numbers when necessary
– State assumptions explicitly
– Round numbers to make your math easier
4. Sanity Check
Product Design

– Do your numbers make sense?

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

Step 1: Ambiguous Information
• Profit or revenue?
Estimation

• Past year? Or average over history?
• Gmail only? Or include Google Apps?
Product Design

Technical

Step 2: Outline Your Approach
(# of users)
Estimation

x
(# clicks / year)
x
( $ / click )
Product Design

Technical

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

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
Product Design

… and so on …

Technical

Step 4: Validate Numbers
• Could revenue be $5 billion?
Estimation

• No, because…
– Google’s annual revenue is ~$40 billion
– $16 / US citizen (not just Gmail users)
Product Design

Technical
How to Solve Tough Problems
1. Ask Questions!
– Questions are more ambiguous than they appear
2. Talk out loud
– Show us how you think
Estimation

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
Product Design

– And make CAREFUL fixes.


Technical
What does a “good coder” do?
• Code in top-left of whiteboard
• Pseudocode first (if necessary)
• Be methodical. Don’t try to rush.
Estimation

• Reasonably Bug Free
– Thorough testing (and careful fixing)
– Check for error conditions
• Clean coding
– Use other functions
Product Design

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


Technical Types of Interview Questions

Coding & Algorithms Object Oriented Design System Design

Pattern Matching
Estimation

Simplify & Generalize

Base Case & Build

Data Structure
Brainstorm
Product Design


Technical Algorithm Qs: Pattern Matching


Pattern Matching
Q: Write code to reverse the order of words
in a sentence.
Estimation

Simplify & Generalize “dogs are cute”
“cute are dogs”

Base Case & Build Similar to: reverse characters in a string.
“dogs are cute”
Data Structure “etuc era sgod”
Brainstorm
Product Design

A: Reverse full string, then reverse each
word.


Technical Algorithm Qs: Simplify & Generalize


Pattern Matching
Q: Design algorithm to figure out if you can
build a ransom note (array of strings) from a
Estimation

Simplify & Generalize magazine (array of strings).

Simplify: what if we used characters instead
Base Case & Build of strings?
 Build array of character frequencies.
Data Structure
Brainstorm
Product Design

Generalize: how we can extend answer to
words?

A: Build hashtable from word to frequency.

Technical Algorithm Qs: Base Case & Build


Pattern Matching Q: Design algorithm to print subsets of set.
{a, b, c}  {}, {a}, {b}, {c}, {a, b},
Estimation

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

S({})  {}
Base Case & Build S({a})  {}, {a}
S({a, b})  {}, {a}, {b}, {a, b}
Data Structure S({a, b, c}) ?
Brainstorm
Product Design

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


Technical Algorithm Qs: Data Structure Brainstorm


Pattern Matching Q: There are 10^10 possible phone #s.
Explain how you could efficiently implement
Estimation

Simplify & Generalize assignSpecificNum(num) and
assignAnyAvailableNum().

Base Case & Build Array (sorted)? Too slow to remove num.
Linked list? Too slow to find specific num.
Data Structure Hash table? Can’t iterate through free nums.
Brainstorm Tree? Ah-ha!
Product Design

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


Technical How To Solve Algorithm Questions


Pattern Matching Compare to similar problems.
Estimation

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

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

Data Structure
Brainstorm Try to apply data structure to solve problem.
Product Design


Technical Whew! All Done!


Pattern Matching
<Gulp> This is a lot of
Estimation

Simplify & Generalize stuff. Do I need to get
everything right?
Base Case & Build

Data Structure
Brainstorm
Product Design


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! {ask to add your name too} • iPhone App
• Resume Review
5 stars! • Mock Interviews
Behavioral

today
$15 Or, stalk me online at…
• twitter.com/gayle
• facebook.com/gayle
• technologywoman.com
Applying

• gayle@careercup.com

today
$25
Process


Cracking the oding interview code chix - oct 2012

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