7 steps to tackling a coding problem

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

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

3. What We Look
For
Things that make you think
01

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

5. 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.

6. gayle in/gaylemcdgayle 6
z
Gayle Laakmann McDowell
What
IS
expected
Be excitedabout hard problems
Drive!
 Keep trying when stuck
 More than just “correct”
Pay attention to me!
Write real code
Showmehowyouthink!

7. Preparation
02

8. gayle in/gaylemcdgayleGayle Laakmann McDowell 8
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

9. gayle in/gaylemcdgayleGayle Laakmann McDowell 9
Preparation
MASTER Big O
ImplementDS/Algorithms
Practicewith interview questions
Code on paper/whiteboard
Mock interviews
PUSHYOURSELF!

10. 7 Steps
Things that make you think
03

11. gayle in/gaylemcdgayle 11
z
Gayle Laakmann McDowell
How
To
Approach
CrackingTheCodingInterview.com“Resources”

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

13. gayle in/gaylemcdgayle 13Gayle Laakmann McDowell
step
Draw an Example
INTERSECTION SIZE: Find #
elementsin common between
two sorted, distinct arrays:

14. gayle in/gaylemcdgayleGayle Laakmann McDowell 14
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

15. gayle in/gaylemcdgayleGayle Laakmann McDowell 15
Ex:Intersection ofTwo Sorted Arrays
Better:
[1, 12, 15, 19, 20, 21]
[2, 15, 17, 19, 21, 25, 27]
 Big
 No specialcases

16. gayle in/gaylemcdgayle 16Gayle Laakmann McDowell
step
Draw an Example
Big Enough
General Purpose
+

17. gayle in/gaylemcdgayle 17Gayle Laakmann McDowell
step
Brute Force / Naive
Stupid&terribleisokay!

18. gayle in/gaylemcdgayle 18Gayle Laakmann McDowell
step
Optimize
Walk through brute
force
Look for optimizations

19. Gayle Laakmann McDowell 19gayle in/gaylemcdgayle
Techniquesto Develop Algorithms
BUD
Space andTime
Do It Yourself

20. Gayle Laakmann McDowell 20gayle in/gaylemcdgayle
(A) Look for BUD
Bottlenecks
Unnecessary work
Duplicated work

21. Gayle Laakmann McDowell 21gayle in/gaylemcdgayle
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

22. Gayle Laakmann McDowell 22gayle in/gaylemcdgayle
What’s unnecessary?
 Ex: a3 + b3 = c3 + d3 (1 <=a,b, c, d<= 1000
 Unnecessary: looking for d
U

23. Gayle Laakmann McDowell 23gayle in/gaylemcdgayle
What’s unnecessary?
 Ex: a3 + b3 = c3 + d3 (1 <=a,b, c, d<= 1000
 Unnecessary: looking for d
U

24. Gayle Laakmann McDowell 24gayle in/gaylemcdgayle
What’s duplicated?
 Ex: a3 + b3 = c3 + d3 (1 <=a,b, c, d<= 1000
 Duplicated: c, d pairs
D

25. Gayle Laakmann McDowell 25gayle in/gaylemcdgayle
What’s duplicated?
 Ex: a3 + b3 = c3 + d3 (1 <=a,b, c, d<= 1000
 Duplicated: c, d pairs
D
c d c3 + d3
… … …
4 31 29855
4 32 32832
4 33 36001
… … …
5 59 205504
5 60 216125
5 61 227106
… … …

26. Gayle Laakmann McDowell 26gayle in/gaylemcdgayle
What’s duplicated?
 Ex: a3 + b3 = c3 + d3 (1 <=a,b, c, d<= 1000
 Duplicated: c, d pairs
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)
… …

27. Gayle Laakmann McDowell 27gayle in/gaylemcdgayle
What’s duplicated?
 Ex: a3 + b3 = c3 + d3 (1 <=a,b, c, d<= 1000
D

28. Gayle Laakmann McDowell 28gayle in/gaylemcdgayle
(B)Space/TimeTradeoffs
Hashtables & other datastructures
Precomputing

29. Gayle Laakmann McDowell 29gayle in/gaylemcdgayle
(C)Do it yourself
Findpermutationsof swithinb

30. gayle in/gaylemcdgayleGayle Laakmann McDowell 30
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

31. Gayle Laakmann McDowell 31gayle in/gaylemcdgayle
(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

32. Gayle Laakmann McDowell 32gayle in/gaylemcdgayle
Techniquesto Develop Algorithms
BUD
Space and Time
Do It Yourself

33. gayle in/gaylemcdgayle 33Gayle Laakmann McDowell
step
Walk Through
Know the variables
andwhen they change

34. gayle in/gaylemcdgayle 34Gayle Laakmann McDowell
step
Write Beautiful Code

35. Gayle Laakmann McDowell 35gayle in/gaylemcdgayle
How toWrite WhiteboardCode
Top-leftcorner
Short Hand Helps
Good style
Modularize (upfront!)

36. Gayle Laakmann McDowell 36gayle in/gaylemcdgayle
ShortHandHelps
Good:
Good Enough &Easier:

37. gayle in/gaylemcdgayleGayle Laakmann McDowell 37
Good Style
Appropriate & ConsistentSpacing
Good Variable Names
BAD

38. gayle in/gaylemcdgayleGayle Laakmann McDowell 38
Modularization

39. gayle in/gaylemcdgayle 39Gayle Laakmann McDowell
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

40. gayle in/gaylemcdgayle 40
z
Gayle Laakmann McDowell
How
To
Approach
CrackingTheCodingInterview.com“Resources”

41. If you forget
everything else
Please remember this
04

42. gayle in/gaylemcdgayleGayle Laakmann McDowell 42
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

43. gayle in/gaylemcdgayleGayle Laakmann McDowell 43
Other Resources
Gayle.com
CareerCup.com
CrackingThe
CodingInterview.com
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