This is the presentation presented by Richard Park and myself at the University of Waterloo on January 30, 2013. These slides contain insights into interviews that we have discovered in our experience both interviewing and being interviewed.

1. Rocking The Tech Interview
Tim Worboys, Sr Manager, Software Engineering
https://www.slideshare.net/TimWorboys/

2. Interviews Conducted: > 400 Interviews Attended: > 100

3. Tech Industry is in Demand
 Job title Software Engineer on LinkedIn this week
– 86,239 in the USA
 Being in Tech you are in High Demand
 Very few candidates get hired (industry average ~1%)
– Don’t take it personally, there are still 86,238 other positions
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4. What to Expect – Interns
 LinkedIn does two interviews for intern candidates
 2 coding questions
– Conducted over the phone
– Hiring committee reviews the interview feedback after each
interview
– We include technical communication and soft skills assessments
during these modules
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5. What to Expect – New College Grads
 Screen by recruiter
 One technical phone screen
 Four types of on-site interviews
– Coding and Algorithms
– Technical Communication
– Design
– Culture fit
 Expect 6-10 onsite interviews
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6. Getting the Interview – Resume Do’s
 Contact Info
 No spelling or grammar errors (Especially in your name)
 Pleasing to eye using bold, italics, etc
– Don’t go overboard it should still be professional
– It’s all about balance
 Write your resume to the job description
– If you don’t have software experience explain how
past experience qualifies you
 Put your graduation year
 Be descriptive enough for previous work experience
 Be relevant
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7. Getting the Interview – Resume Do’s
 Highlight projects you have done
 Show that you are well rounded
 Focus on experience relevant to the position
 Participate in Hackathons
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8. Getting the Interview – Resume Don’t’s
 Write Paragraphs
 Have more than three lines per bullet
 More than 1-2 pages
 Be vague
 Include outdated or irrelevant information
if you have more relevant/recent
experience
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ReSUMe

9. Resume Evaluations
 How do we pick our interns?
– Work Experience
 Previous employers
 Relevant job experience or skills used
– Education
 Marks received
 Relevant courses taken
 Improvement over time?
– X-factor
 Totally subjective indicators
 Participated in hackdays?
 Side projects?
 Leadership roles
– Potential
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10. First Impressions
 Actively use LinkedIn
– Tons of companies recruit actively on LinkedIn
 Be respectful
 Don’t be confrontational
 Don’t act like it’s a waste of your time
 Don’t take failure personally
– You may not be a fit today, learn and try again
– Interview processes are designed to have more false negatives
than false positives
– Most companies let you re-interview after 12 months, some 6
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11. First Impressions
 Be presentable
– Suits good, not always necessary
– Check with interviewer first.
 What not to wear
– ‘engineer’ clothes (we’re slobs)
– Definitely do not bring a sword
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12. The Interview
 Know what you are interviewing for
– Will often test on specifics of the role you are applying for
 Use LinkedIn
– Research companies and interviewers
– For figuring out questions interviewer may ask
 Be calm
 Be friendly
– Often one of the criteria being observed, if not happy interviewers
generally grade easier
 Be enthusiastic about what you do
– Have a good idea about what you want to do
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13. The Interview
 Ask your interview for:
– Clarifications
– How functions work (consider them Google)
– Hints if you’re really stuck
 Start with the brute force answer, and see how you can
improve it from there
 Think before you start coding – have a game plan
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14. Question Types
 Interview questions generally fit in several categories:
 Soft Skill Questions
– Questions not based on any concrete skills. i.e. “greatest
weakness”
 Puzzle Questions
– Puzzles, tricks, riddles, etc
 Design Questions
– Re-design product X or architect system
 Coding and Algorithm Questions
– Coding style, algorithms, etc.
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15. Soft Skill Questions
 Common questions:
– “What is your greatest weakness?”
– “Tell me about a time that you overcame adversity?”
 Good answer is a personal and honest answer that
seems like you’ve given thought to the question.
– If it’s a weakness, say how you’re correcting it
 Don’t be cliché
– I’m a perfectionist
 You should be prepared for these types of questions
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16. Puzzle Questions
 ‘Aha’ Questions
– Worst type of questions. You either get it or you don’t.
– Don’t give up, plug away until your interviewer gives a hint or
steers you away
 Open-ended No-answer Questions
– Figuring out if it’s an open-ended question can be difficult
– Keep talking, don’t fixate.
– Sometimes you need to think ridiculously
 Work-through Questions
– Logically estimate
– If you’re making estimates use nice round numbers (ex. 100
instead of 77)
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17. Puzzle Questions Examples
 ‘Aha’ Questions
– You have two non-uniform ropes (half the rope burnt doesn’t
mean half the time) and a bunch of matches. Each rope takes an
hour to burn, but the two ropes are not identical. How can you
measure exactly 45 minutes?
 Open-ended No-Answer Questions
– You are in a maze and at the center of the maze is a trophy.
There is a tree with a rope that you can see nearby. However,
there are two angry apes that if they spot you in the maze will
throw you out, how do you get the trophy?
 Work through Questions
– Estimate # of dogs in purses in North America
– Can a tower of loonies high as empire state building fit in this
room?
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18. Re-Design Questions
 “Re-design something that exists” Question
– Eg. Design an elevator, Design a coffee machine
 Think about how you would use what you are designing
 Design to fix issues you have with current solutions
 Think about the users
 Be open-minded. Think outside the box, even if a bit
ridiculous.
 Think about costs and practicality
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My failed designs for
future transportation
system

19. Architectural Design Questions
 Build a system
 Use box diagrams
– Services
– Components
– Interactions
 Remember everything can and will fail
– Disks, machines, power, network, etc
 Talk out your solution
– Interviewer is there to assess your thinking abilities, not your
ability to be quiet
 Understand constraints (money, scale, practicality)
 You will likely feel like you’re doing a bad job – you
probably aren’t
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20. Coding and Algorithm Questions
 The bulk of questions we ask are Coding and Algorithm
Questions
 What we’re looking for
– Understanding of the problem
– Asking the right questions
– Completeness of solution
– Analytical abilities
– Communication
– Coding abilities
– Can we work with you??
 Several bag of tricks can be used for different types of
questions.
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21. Coding Languages
 Language is important to some, not for others
– Should know at least one well used language
– Read the job posting, and brush up on that language
– Be honest about the programming languages you know.
– Ask the recruiter about language interview is in
 C++
– Read C++ Faq Lite!
– Remember not to make a leak, leave things dangling or form diamonds
 Java
– Knowing how Garbage Collection really useful
– Java 1.5+ has for-each, generics, concurrency package. Knowing them
can speed up time during interview
 Everyone should know SQL
– Just know the basic syntax. Oracle, MySQL, SQLServer all have
differences.
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22. What should I do for Coding Questions?
 Think before you write
– Diagrams, pseudo-code, talk-it-out, etc
– You should know your code well when written
 We expect you to find your errors quickly
 Do not make uneducated guesses
 Ask what functions will be given to you by the interviewer
 Unsure about an API, just ask!
 Write your own test cases without prompting
 Know when your interviewer is trying to steer you in a
different direction
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23. Coding Style
 Use short, but descriptive names for variables
 Add comments, especially on computer
 Think completeness in code
– C/C++ Malloc or new? Release or delete.
– In OO, constructors (destructors?)
– Opening input stream? Close it when done
– Public/Private/Protected member accessors
 Exceptions often better than return codes
 Wrapping often better than inheriting
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24. Our Bag of Tricks
 Most problems are just modifications of other problems
 Having a bag of common tactics and knowledge can put
you ahead.
– Many seem obvious, but surprising how many people don’t know.
 Split into several categories:
– data structures
– common algorithms
– number theory
– networks
– concurrency
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25. Data Structures You Should Know
 Hashtable
– The most important data structure (besides Vectors)
– amortized O(1) insert, removal, search
– Hash the key, map key to array index
– Know different implementations of it
 Double Hash
 Linked
 Linear Probing
– Know the limitations
 Uses more memory (usually 0.75 the # entries extra)
 Bad hashing function causes lots of collisions = bad
– Want lookup table? dictionary? Of course you do.
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26. Data Structures You Should Know
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 Trees
– Remember they can be unbalanced, not always binary
 LinkedList (doubly-singly)
– Useful in interviews, not so much in real life
 Heap
– If you need a priority list, or top-n elements
 Graph (Nodes, Edges)
– Can store as adjacency list, sets of nodes and edges, matrix
 Others:
– Stacks, Queues, Circular Buffer
 Know each one’s strengths and weaknesses

27. Algorithms You Should Know
 Sorting Algorithms
– Heap Sort, Merge Sort, Insertion Sort, Quick Sort, Bubble Sort,
Bucket Sort
 O(nlog(n)) for most sort.
 Quick sort runtime actually varies
 Consider bucket (radix) sort (O(n)) if sorting dense integer ranges
 Searching
– Have a sorted array?
– Items not sorted? Consider sorting them.
 O(nlogn) one time, O(logn) search
– hashtable and lookup
 O(n) one time, O(1) search
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28. Algorithms You Should Know
 Tree Traversals
– BFS
 Use a Queue
– DFS
 Stack or Recursion
 Dykstra’s Shortest Path
 Intersection of lists
– Sorted lists, it’s O(n) with O(1) additional memory.
– With unsorted list and no additional memory, sort O(nlogn)
– With unsorted list and additional memory, lookup table with
smallest list (O(n))
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29. Algorithms Extras
 Often trade off between memory and processing
– Store if you think you will repeat calculations
 Consider pre-calculating results and quickly looking up
 Recursion has cost
– Convert to iterative with stack, often not worth it
 KNOW RUN TIME COMPLEXITY
– Obviously n3 > n2 > n log n > n > 1
– Knowing the complexity of your solution can indicate whether you
can do better. If you have to sort, can’t do better than n logn
– Rarely is a n! or xn the correct solution, look for a trick!
 Practice.
– Questions are often different mutations of other questions.
– The more you see, the more tactics you will have
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30. Number Theory
 Floating points
– Single: sign - 1, exponent - 8, mantissa - 23
– Double: sign - 1, exponent - 11, mantissa - 52
– Precision Errors
 Two’s Complement
– How to convert (invert, add 1)
 Endianness (big and little)
 Bit Shift tricks
– >>: Divide by 2
– <<: Multiply by 2
– Consider the sign when >> a negative number
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31. Networks/Distributed
 TCP, UDP, HTTP
 Fallacies of distributed computing and networks
– Networks are unreliable
– Latency is not zero
– Bandwidth is finite
– Networks are not secure
– Topologies change
 How to achieve consistency and reliability
– Master/slave
– Leader elections (quorum)
– Replication
 RPC Protocols
– SOAP, REST, Thrift, Protobuffs, Avro, etc.
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32. Concurrency
 Know the basics
– Spin Lock, Mutex, Monitor, Semaphore, Signals, Synchronization
– These questions are good because they require more thinking
and less pattern matching
– Know which variables need to be shared, and protect them
 Know producer/consumer problem
– Need common queue or buffer
– Java has it easy (BlockingQueue)
 Know the reader/writer problem
– Reads blocks writes, but not reads
– Writes blocks writes and reads
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33. Misc Coding Stuff
 Know when to use disk
– Remember that disk is an option, not just RAM
– Sequential reads/writes good, Random seeks bad
 Buffer Reads/Writes
– Good practice, makes things more efficient
 Check for off by one errors
 Use java (or high level language) when given the option
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34. Other Hints
 Be calm
 Know what you are interviewing for
– You will often be tested on specifics of the role you are applying for
 Use LinkedIn
– For getting jobs
– Research companies and interviewers
– For figuring out questions interviewer may ask
 Be friendly
– Often one of the criteria being observed, if not happy interviewers
generally grade easier
 Be enthusiastic about what you do
– Have a good idea about what you want to do
 When in doubt, ask for clarifications
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35. Conclusion
 Remember your data structures (hashtable!)
 Brush up on languages
 Be friendly and calm
– Don’t be nervous, you are in demand
 Prepare
– Do as many problems as you can
 Keep talking, but not too much
 If you’re an intern, ask if you can sit in on a few
interviews.
 Ask when you can reapply if you don’t get an offer and do
so!
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36. Want More?
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$16
Practice Websites
• https://leetcode.com/
• https://www.hackerrank.com/

37. Questions
 Given a binary search tree, write a function to find the kth
smallest element in the tree.
 Note: You may assume 1 <= k <= total nodes in tree
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2
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 If k = 2, result = 2 (2 is second smallest)
 If k = 1, result = 1 (1 is smallest)
 1) Brute force (extra memory
 2) No extra memory
 3) O(1) get

38. Questions
 Remove duplicates from an unsorted linked list
 Implement a queue using stacks; write enqueue and
dequeue functions
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39. https://www.slideshare.net/TimWorboys/