Cracking the Coding Interview - 7 steps - Udacity

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)

What We Look
For
Things that make you think
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!

7 Steps
Things that make you think
03

z
How
To
Approach
CrackingTheCodingInterview.com“Resources”

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

step
Draw an Example
INTERSECTION SIZE: Find #
elementsin common between
two sorted, distinct arrays:

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 commonelement, same index

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

step
Draw an Example
Big Enough
General Purpose
+

step
Brute Force / Naive
Stupid&terribleisokay!

step
Optimize
Walk through brute
force
Look for optimizations

Techniquesto Develop Algorithms
BUD
Space andTime
Do It Yourself

(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]
 Brute Force: O(A * B)
  Bottleneck:O(B) tosearch
 Binary Search Algorithm: O(A log B)
  Bottleneck:O(logB)tosearch
 Sorted Merge: O(A + B) 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

(C)Do it yourself
Findpermutationsof swithinb

find abbcd in
b a b c d b a e f d b b a c b d d f a e
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

(C)Do it yourself
Findpermutationsof swithinb
 s = abbcd
 b =
Findthem!
 … now how didyou actuallydoit?
b a b c d b a e f d b b a c b d d f a e

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

step
Walk Through
Know the variables
andwhen they change

step
Write Beautiful Code

How toWrite WhiteboardCode
Top-leftcorner
Short Hand Helps
Good style
Modularize (upfront!)

ShortHandHelps
Good:
Good Enough &Easier:

Good Style
Appropriate & ConsistentSpacing
Good Variable Names
BAD

Modularization

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
CrackingTheCodingInterview.com“Resources”

If you forget
everything else
Please remember this
04

Please please please please
Create example
 Big (tinyisuseless)
 Generic(nota specialcase)
Walkthrough it
 Figureouttheoutputforthatoneinput
 (Don’tworryaboutalgorithms/ implementation)
DO NOT CODE UNTIL YOU’RE READY
 100%surethatyouknowwhatyou’redoing
 100%surethatyourinterviewwantsyoutocode

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

Cracking the Coding Interview - 7 steps - Udacity

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