Technical Interviews

1. Technical Interviews Brad Swerdfeger – April 24, 2009

2. Why do you care? • Interviewing method for premiere tech companies. • Microsoft • Google • Apple • If you go into industry, you should be prepared. • The questions are challenging and fun!

3. Disclaimer I’m not saying that this is how companies should interview people, but rather how they do interview people. Hopefully this is helpful if you do get an interview.

4. Outline • History • Types of Interviews • Problems & Techniques/Tips • Behavioural • Programming • Design • Logic & Geometry • ‘Impossible’ Questions • My experience @ Microsoft • Suggested Reading

5. History • 1957: William Shockley • Helped invent the transistor (Bell Labs) • Big Idea: Build transistors with silicon • Interviewing Jim Gibbons (Stanford PhD.) • Pulls out a stopwatch • There’s a tennis tournament with one-hundred and twenty-seven players... • Rationale: • Tonnes of reasons for and against. We can talk about them later. • It’s about avoiding False Positives • For now, what matters is that you survive.

6. Types of Interviews • @ Microsoft, but captures the gist: • Software Developer • Programming problems • Program Manager • Design/Behavioural problems • Will have to code something • Software Dev/Test • Programming problems • Interested in boundary conditions/special cases.

7. Problems • Behavioural • Programming • Design • Logic & Geometry • ‘Impossible’ Questions

8. Behavioural Problems • Your typical HR questions but with a twist. • “Tell me a time when...” • Shows that you’ve thought about and learned from past experiences. • Examples: • Tell me about a difficult decision you've made in the last year. • Give me an example of when you showed initiative and took the lead. • Give me an example of a time when you motivated others.

9. Tips for Behavioural Problems • Get a list of questions and write out answers to them beforehand! • Not for memorization. • To make you think and give you a repertoire of experiences. • Failed experiences: • Make sure you talk about: • What went wrong and why. • What you learned. • What you would do differently. • Don’t be hypothetical. Be concrete.

10. Problems • Behavioural • Programming • Design • Logic & Geometry • ‘Impossible’ Questions

11. Programming Problems • The meat of a developer interview. • Can code in any language • Interviewer may insist on one that is on your resume • Likely that pseudo-code is fine. • Concerned about: • What clarification questions you ask • How you go about solving the problem • Planning/Implementation/Testing/Iteration • Your thought process

12. Programming Problems • Linked Lists • Trees/Graphs • Arrays and Strings • Recursion • Concurrency • OO Programming • Databases • Other

13. Example Problems: Linked Lists • Implement a stack in C using a linked list • Tests basic understanding of pointers • Maintain a linked list tail pointer • Tests handling of special cases • Mth-to-last element of a linked list • Cycle detection

14. Example Problems: Linked Lists

15. Example Problems: Trees/Graphs • Preorder Traversal • Tests knowledge of recursion. • Now with no recursion... • Lowest Common Ancestor • Tests knowledge of simple data structures

16. Example Problems: Arrays/Strings • Find the first non-repeated character. • Tests knowledge of data structures and code optimization. • Remove specified characters • Reverse words • piglet quantum -> quantum piglet • Tests pointer manipulation • Integer/String conversions • Tests knowledge of data representation, math tricks.

17. Tips for Programming Problems • Ask clarification questions • Vocalize • Come up with multiple answers – trade-offs. • Start off with an example and discuss solution in terms of example. Then move to general case. • Write pseudo-code first! • Discuss complexity • Time • Space • TEST your solution. • Don’t forget boundary cases.

18. Problems • Behavioural • Programming • Design • Logic & Geometry • ‘Impossible’ Questions

19. Design Problems • Meat of Program Manager or User Experience interviews. • Design a... • Concerned with: • Creativity • Feature prioritization/trade-offs • Design process knowledge • Customer/End User advocacy • Salesmanship • Design Rationale

20. Design Problem Examples • Design Bill Gates’ washroom • Design a 21st century... • Fridge • Parking meter • Kitchen timer • <Insert Consumer Electronic> • Design a spice rack for a blind person • How would you explain Excel to your grandmother?

21. Design Problem Tips • ASK QUESTIONS! • Always consider the user. • Who are they? • What do they do? • What do they like? • Think of the customer vs. the end user • How can you save the customer money? • Be good at drawing on a whiteboard. • Stick to your guns! • Stay simple and elegant.

22. Problems • Behavioural • Programming • Design • Logic & Geometry • ‘Impossible’ Questions

23. Logic & Geometry Questions • Most controversial. • Makes you: • Question assumptions • Think creatively • Think logically to the point where it’s inhumane. • Tests intelligence? • Or just ability to solve logic puzzles... • Either way, you need to learn how to solve them, just in case.

24. Logic Puzzle Types • Spatial Reasoning • Probability • Measuring • Computer Science – Disguised! • Recursive Thinking • River/Bridge Crossing • Chase Questions • So many more...

25. Logic Puzzle Examples • I could spend hours giving examples and solution techniques. • Ian’s UDLS redux? • Future UDLS? • Here are a few...

26. Logic Puzzle Examples Four people must cross a rickety footbridge at night. Many planks are missing, and the bridge can hold only two people at a time (any more than two, and the bridge collapses). The travelers must use a flashlight to guide their steps; otherwise they're sure to step through a missing space and fall to their death. There is only one flashlight. The four people each travel at different speeds. Adam can cross the bridge in one minute; Larry in two minutes; Edge takes five minutes; and the slowest person, Bono, needs ten minutes. The bridge is going to collapse in exactly seventeen minutes. How can all four people cross the bridge?

27. Logic Puzzle Examples • You have b boxes and n dollar bills. Seal the money in the boxes so that, without thereafter opening any box, you can give someone any requested whole amount of dollars, from 0 to n. What are the restrictions on b and n? • You have 26 constants, labelled A through Z. Let A equal 1. The other constants have values equal to the letter's position in the alphabet, raised to the power of the previous constant. That means that B (the second letter) = 2A = 21 = 2. C = 3B = 32 = 9, and so on. Find the exact numerical value for this expression: (X-A) * (X-B) * (X-C) * ... (X-Y)*(X-Z)

28. Logic Puzzle Examples There are four dogs, each at a corner of a large square. Each of the dogs begins chasing the dog clockwise from it. All of the dogs run at the same speed. All continuously adjust their direction so that they are always heading straight toward their clockwise neighbour. How long does it take for the dogs to catch each other? Where does this happen?

29. Logic Puzzle Examples (my fav) Every man in a village of fifty couples has been unfaithful to his wife. Every woman in the village instantly knows when a man other than her husband has philandered (you know how small towns are) but not when her own husband has ("always the last to know"). The village's no tolerance adultery statute requires that a woman who can prove her husband is unfaithful must kill him that very day. No woman would dream of disobeying this law. One day, the queen, who is known to be infallible, visits the village. She announces that at least one husband has been unfaithful. What happens?

30. Logic Puzzle Examples You have five jars of pills. All the pills in one jar only are "contaminated." The only way to tell which pills are contaminated is by weight. A regular pill weighs 10 grams; a contaminated pill is 9 grams. You are given a scale and allowed to make just one measurement with it How do you tell which jar is contaminated?

31. Tips for Logic Puzzles • Read lots of examples and lots of solutions. • Try to figure them out first • Classify types of questions. • Question assumptions. • Other tips: • Decide what kind of answer is expected. (Monologue vs. Dialogue). • Whatever you think of first is wrong. • Forget you ever learned calculus. • Big questions usually have simple answers. • Simple questions demand complicated answers. • Perfectly logical beings are not like you and me. • Reason about disjunctions.

32. Problems • Behavioural • Programming • Design • Logic & Geometry • ‘Impossible’ Questions

33. ‘Impossible Questions’ • Designed to overwhelm you. • Tests for: • Perseverance • Composure • Problem solving skills • Small, manageable steps • You don’t have to get the right answer! • Just be intelligent during your reasoning process.

34. ‘Impossible Question’ Examples • How long would it take to move Mount Fuji? • How much water flows through the Mississippi River annually? • How many gas stations are there in the United States? • If you could remove any state, which one would you remove? • How would you locate a specific book in a big library? There's no cataloguing system and no librarian to help you. • How do they make M&Ms?

35. ‘Impossible Question’ Tips • Don’t panic! • Attack the problem methodically. • Strike up a dialogue with the interviewer. • Practice making ‘back of the envelope’ estimates. • E.g. How many hours does a grad student spend working on their thesis in two year? • Be strictly rational.

36. General Interview Tips • Be yourself. • *Take suggestions from interviewers* • Ask questions! • Realize that your interviewers were in your shoes before. • They’re just people. Smart people who want to hire you. • Speak assertively and confidently. • Be self-critical, but not too much. • Don’t be arrogant!

37. My Experience at Microsoft • Sent resume to campus recruiter. • Got invited for phone interview. • 30 minute interview with design/programming questions. • ~3 weeks later, invitation to fly to Redmond. • Asked about career objectives • ~3 weeks after that, was in Redmond.

38. Trip to Microsoft Campus • All expenses paid! • 35 minute flight to Seattle. • Rented a car for me. • Swanky hotel room. • King sized bed • HD TV • $75 a day for meals (room service!) • Paid long distance calls

39. Interview Day • Night before – impossible to sleep. • Day off – drank a shitload of coffee, had a big breakfast and drove to campus. • Did a practice run driving there the night before. • Building 19 is SWEET. • Played with the MS Surface with other interview candidates to break some tension and kill some nerves. • Met with a recruiter. • Briefed me about the day.

40. Interviews • Interviewed for a PM position with Office. • Do between 3 and 5 • If you do 3, you didn’t get the job. • I did 5: • Outlook PM 1 • Outlook PM 2 • Sharepoint PM 2 • Sharepoint GPM (Hiring manager) • Enterprise Search GPM (Objective viewpoint)

41. Interview 1 • Really, super nice guy. • Been there 3 years, serious number of patents. • Q1: What do you know about the PM position? • Q2: Write a program to solve Boggle. • Q3: Design a kitchen timer that times multiple things. • Went well, gave me lots of tips.

42. Boggle

43. Interview 2 • PM 2 with Outlook. • Designs the location of buttons/menu items. • Q1: Tell me about yourself (I couldn’t print your resume). • Q2: Why PM and not Usability Designer? • Q3: Design a 21st century parking meter for the city of Vancouver • Went OK... But she was merciless with design.

44. Interview 3 • Sharepoint PM 2 (~90 minutes) • Really nice Irish guy. • Q1: Tell me about your experiences working on a team. • Q2: Design a 21st century fridge. • Went out to lunch with him • Asked him all about Sharepoint.

45. Interview 4 • Group Program Manager (Sharepoint) • CRAZY nice guy. I want to work for him. • Q1: Tell me about yourself. • Q2: (puts code on board) – it was a recursive formulation of the Fibonacci sequence in C. • Trace it. • Make it iterative . • How else could you do this? • Q3: Design an alarm clock for a college student. • Q4: Give me 3 things you hate about Office and how would you make them better? • Q5: Sell me something cool (now something else) • What’s the next feature for that? And the next?

46. Interview 5 • Group Program Manager @ Enterprise Search • Really philosophical dude • Office was really FengShui (Banzai trees ...) • Q1: Why software? • Q2: Why PM and not Usability Designer? • Q3: How would you explain how the internet works to your grandmother? • Q4: TiVo wants to break into the car market. You are a PM for TiVo, design a product. • Spent 2 hours on this!

47. Conclusion • It was a long freaking day, but I’m glad that I did it.

48. Suggested Reading • MUST READ: • How would you move Mount Fuji? – William Poundstone • Programming Interviews Exposed -- John Mongan, Noah Suojanen, Eric Giguère • PMs • The Art of Program Management – Scott Berkun • The Design of Everyday Things – Donald Norman • Developers: • Programming Pearls – Jon Bentley • Probably more... I was interviewing for PM.

49. Thanks!