Cracking the Coding interview (College)

GayleL. McDowell | Founder/ CEO
gayle in/gaylemcdgayle
Cracking the Coding
Interview
Harvard
CareerCup.com

gayle in/gaylemcdgayleGayle Laakmann McDowell 2
Hi! I’m Gayle LaakmannMcDowell
Author Interview Coach Interview Consulting
<dev> </dev>
(CS) (MBA)

Gayle Laakmann McDowell 3gayle in/gaylemcdgayle
Yes! Slidesare online!
Gayle.com
 Click“Events”

Early Preparation
Landing an interview
00

How to Get an Interview
Your Background
 Education
 Work Experience
 Projects
 Github/ OnlineProfile
Make a great resume
McDowell | CareerCup.com

Did I mention…
PROJECTS???

gayle in/gaylemcdgayle 7Gayle Laakmann McDowell
How We
Review
Resumes
1. Pull resume out of giant stack
2. Spot-check:
companies, projects, etc.
3. Skim bullets to see if you’ve written real
code.
4. Go tonextresume & whine abouthowmany
moreyouhaveleft.
InterviewReject
“Glancedat,”not
read.
15seconds

How CS ResumeShouldLook
Short
(1 – 2 line bullets)
3 – 4 Projects
Courses & independent
Finished or unfinished
List of Technical Skills
Short! Cut the “fluff.”
GPA if at least 3.0
max (in-major, overall)
One Page Only!
Unless > 10 years exp.
A Real Resume Format
with organized columns
Focus on Accomplishments
not responsibilities
Observe: No Objective!
Objectives / summaries
are almost always useless.

Talking
to
Recruiters
Show:
 What you’vedone(mobileapp?Show
it!)
 What you’reexcitedabout
Have a “pitch” ready
Weird is okay
 (arrogantisnot)

Behavioral Questions
The soft squishy stuff.

The Pitch /Resume Walk-Through
• Showsof success
• Prompt the
interviewer
• Hobbies

Your Past Work
 1 – 2 Hard Projects
 Hard/ cool
 Youwerecentral
 Technical depth
 All Past Work
 Challenges,architecture,
tradeoffs,mistakes,successes,
motivations
 Whatdid YOU do?

Technical
Questions
Why why why why why why meeeee
02

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

gayle in/gaylemcdgayle 15
z
Gayle Laakmann McDowell
What
Really
Happens

z
What
Really
Happens
Knowledge Questions
 +Coding
Design/Scalability
 +Coding
Algorithms/Problem Solving
 +Coding

Knowledge Questions
How do indices work in SQL?

Knowledge Questions
If you list it, know it If you don’t know it,
admit it
 Deriveitifpossible.

Design
How would you design TinyURL?

z
How
To
Approach
W
W
Y
D
A
W
hat
ould
ou
o
t
ork

z
How
To
Approach
S
K
I
R
cope
eycomponents
dentify issues
epair

z
How
To
Approach
① Scope the Problem
 Askquestions
 Make appropriateassumptions
② Define Key Components
 Can besomewhatnaïve
③ Identify Issues
 Bottlenecks,tradeoffs
④ Repair & Redesign
DiscussTop->Down

How to Act
DRIVE
 Leadtheprocess
 Be openaboutissues
TEAMWORK
 Beopentofeedback
 Tweak asnecessary

z
How
To
Prepare
Read about design of major
companies
 Twitter,Facebook,Quora,Google,etc.
 ThinkaboutWHY they’redesigned
thatway
Learn/review key concepts
 Taskqueues,databases,sharding,etc.
Practice questions

Algorithm Preparation
Problem solving, not puzzles!

Why?
Strong CS
fundamentals
Analytical skills
Make tradeoffs
Push throughhard
problems
Communication
How you think

Essential Knowledge
Data Structures Algorithms Concepts
ArrayLists Merge Sort BigO Time
Hash Tables QuickSort BigO Space
Trees(+Tries) Breadth-FirstSearch Recursion
Graphs Depth-FirstSearch Memoization/ Dynamic
Programming
Stacks/ Queues BinarySearch
Heaps

Preparation
ImplementDS/Algorithms
MASTER BigO
Practice with interviewquestions
Code on paper/whiteboard
Mock interviews
PUSHYOURSELF!

Solving Algorithms
How to… attempt to solve a hard problem

z
What
is NOT
expected
To know the answers
To solve immediately
To code perfectly
(It’snice.Itjustdoesn’t
happen*.)
*Okayfine.Ithappenedonce,in2000+hiringpackets.

z
What
IS
expected
Be excitedabout hard problems
More thanjust “correct”
Drive!
Keeptrying when stuck
Write real code
Showmehowyouthink!

z
How
To
Approach
CrackingTheCodingInterview.com“Resources”

step
Listen (for clues)

What’sthe clue?
Anagram server
 Ex: rates ->aster, stare, taser, tears
Clue:why is it ona server?

step
Draw an Example
Big Enough
General Purpose
+

Ex:Intersection ofTwo Sorted Arrays
Most people draw somethinglike this:
[1, 12, 15, 19]
[2, 12, 13, 20]
 Toosmall
 Toospecial-case-y
• same size, one common element, sameindex

Ex:Intersection ofTwo Sorted Arrays
Better:
[1, 12, 15, 19, 20, 21]
[2, 15, 17, 19, 21, 25, 27]
 Big
 No specialcases

step
Brute Force / Naive
Stupid&terribleisokay!

step
Optimize
Walk through brute
force
Look for optimizations

Techniques to Develop Algorithms
Optimize
A. BUD
B. Space/time
C. Doityourself
Solve
D. Recursion
E. Solve “incorrectly”
F. Other data structures
Pushyourself!

(A) Look for BUD
Bottlenecks
Unnecessary work
Duplicated work

What’s the bottleneck?
 Ex: countingthe intersection
[1, 12, 15, 19, 20, 21]
[2, 15, 17, 19, 21, 25, 27]
 Bottleneck:searching
B

What’s unnecessary?
 Ex: a3 + b3 = c3 + d3 (1 <=a,b, c, d<= 1000
 Unnecessary: looking for d
U

What’s duplicated?
 Ex: a3 + b3 = c3 + d3 (1 <=a,b, c, d<= 1000
 Duplicated: c, d pairs
D

 Ex: a3 + b3 = c3 + d3 (1 <=a,b, c, d<= 1000
D
c d c3 + d3
… … …
4 31 29855
4 32 32832
4 33 36001
… … …
5 59 205504
5 60 216125
5 61 227106
… … …

 Ex: a3 + b3 = c3 + d3 (1 <=a,b, c, d<= 1000
D
c3 + d3 (c, d)
… …
29855 (4, 31)
32832 (4, 32),(18, 30)
36001 (4, 33)
… …
205504 (5, 59)
216125 (5, 60),(45, 50)
227106 (5, 61)
… …

 Ex: a3 + b3 = c3 + d3 (1 <=a,b, c, d<= 1000
D

(B)Space/TimeTradeoffs
Hashtables & other datastructures
Precomputing

Space/Time Tradeoffs  Precomputing
 Find rectangle at origin w biggest sum
6 5 -9 2
-2 -5 -2 7
3 -2 10 13
-8 -3 1 -2
 Brute force: compute all rectanglesand sums

 Find rectangle with biggest sum
6 5 -9 2
-2 -5 -2 7
3 -2 10 13
-8 -3 1 -2
-+ + 10=

 Find rectangle with biggest sum
6 5 -9 2
-2 -5 -2 7
3 -2 10 13
-8 -3 1 -2
-+ + 13=

(C)Do it yourself
Findpermutationsof swithinb
 s = abbc
 b = babcabbacaabcbabcacbb
Findthem!
 … now how didyou actuallydoit?

Techniques to Develop Algorithms
Optimize
A. BUD
B. Space/time
C. Doityourself
Solve
D. Recursion
E. Solve “incorrectly”
F. Other data structures
Pushyourself!

(D) Recursion/ Base Case & Build
Subsets of a set
 {}  {}
 {a}  {}, {a}
 {a, b}  {}, {a}, {b}, {a, b}
 {a, b, c}  …
Subsets of {S1…Sn-1} + Sn to each
• Careful!“This sounds recursive” is 50%
accurate
• Bottom-up approach, top-down
implementation

(E) Solve “incorrectly”
① Develop incorrectsolution
② Identifywhy preciselyit’s incorrect
③ Repair
④ (& Repeat)

(E)Solve “incorrectly”
Random node in BST
Try: flipcoin
Coin=Heads
 Branch Left
Coin=Tails
 Branch Right

Try: random number in {0, 1, 2}
R=0
 Branch Left
R=2
 Branch Right
R=1
 Return root

Try:
 Return rootwith1/n probability
 Then flipcoin(heads left,tails->right)

Try: pick random # 0 throughn-1
R=0
 Return root
R>left.size
 Branch right
1<=R<=left.size
 Branch left

(F) Other Data Structures
Giving outphone numbers
 “I wantany availablenumber”
 “I wantthisnumber”
Try: sorted array?Sorted linkedlist?Hashtable?
BST?

step
Walk Through
Know the variables
andwhen they change

step
Write Beautiful Code

How to Write WhiteboardCode
Write straight
Top-leftcorner
Use arrows if needed
Error cases / TODOs
Good variables
Modularized
Languagechoiceisuptoyou!

Modularization

step
Testing
FIRST Analyze
 What’sitdoing?Why?
 Anythingthatlooksweird?
 Errorhotspots
THEN use test cases
 Smalltestcases
 Edgecases
 Bigger testcases

Final Thoughts
And questions
03

ClosingAdvice
Do projects
Study for your interviews
Chaseinterviews
… but don’t chase money
Check-inon your career.
 Isthiswhatyouwanttodowithyourlife?

z
It’s done
for a
reason!
Be a great teammate.
Be a great engineer.

Other Resources
Gayle.com
CareerCup.com
CrackingThe
CodingInterview.com
Or, follow me online
• facebook.com/gayle
• twitter.com/gayle
• gayle.com
• gayle@gayle.com
• quora.com

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