Cracking the Coding interview (Abbreviated) - aug 2016

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

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

Evaluation
What it’s all about
01

Gayle Laakmann McDowell 4gayle in/gaylemcdgayle
Why?
Analytical skills
How you think
Make tradeoffs
Pushthrough hard
problems
Communication
Strong CS fundamentals

gayle in/gaylemcdgayle 5
z
Gayle Laakmann McDowell
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
Drive!
 Keep trying when stuck
 More than just “correct”
Pay attention to me!
Write real code
Showmehowyouthink!

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

Preparation
MASTER Big O
ImplementDS/Algorithms
Practicewith interview questions
Code on paper/whiteboard
Mock interviews
PUSHYOURSELF!

z
How
To
Approach
CrackingTheCodingInterview.com“Resources”

gayle in/gaylemcdgayle 12Gayle Laakmann McDowell
step
Listen(for clues &details)

step
Draw an Example
Big Enough
General Purpose
+

step
Brute Force / Naive
Stupid&terribleisokay!

step
Optimize
Walk through brute
force
Look for optimizations

step
Walk Through
Know the variables
andwhen they change

step
Write Beautiful Code

step
Write Beautiful Code
RealCode
with
GoodStyle
and
UpfrontModularization

Modularization

Modularize(Upfront!)
I’ve learned
nothing.

step
Testing
FIRST Analyze
 What’s it doing? Why?
 Anything that looks weird?
 Errorhot spots
THEN use test cases
 Small test cases
 Edge cases
 Biggertest cases
BUT…
 Test code, notalgorithm
 Think as you test
 Think before you fix

z
How
To
Approach

Solving &
Optimizing
4 Optimization/Solving Techniques
04

step
Optimize
Walk through brute
force
Look for optimizations

Techniquesto Develop Algorithms
BUD
Space and Time
Do It Yourself
Recursion

(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 at origin w biggest sum
6 5 -9 2
-2 -5 -2 7
3 -2 10 13
-8 -3 1 -2

 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

find abbc in
babcabbacaabcbabcacbb

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

(D)Recursion
 Use, but don’t cling to, recursion
“instinct”
 Trybottom-up
 “Backtracking”
 Draw call-tree
 Derive runtime
 Find repeated subproblems
 Subsets of a set
 {} {}
 {a}{},{a}
 {a,b} {},{a},{b},{a,b}
 {a,b, c} …
 Subsets of {S1…Sn-1} +Sn to each

Techniquesto Develop Algorithms
BUD
Space and Time
Do It Yourself
Recursion

z
How
To
Approach

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

What Now?
Book signing, photos, etc. [withme!]
Mock interviews [withAWS!]
Code challenge [online!]
hr.gs/mockathon

Cracking the Coding interview (Abbreviated) - aug 2016

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