Cracking the Coding Interview

1. Cracking the Coding Interview Advice and Strategies for Software Engineering and PM Interviews Gayle Laakmann McDowell Founder / CEO, CareerCup.com Author of The Google Resume and Cracking the Coding Interview McDowell | CareerCup.com | Women Who Code Aug 2012

2. My Background • Software Engineer @ GOOG, MS & Apple • 3 Years on Google Hiring Committee • Interviewed 150+ candidates • Founder of CareerCup.com • 8000+ tech interview questions • Author • Cracking the Coding Interview • The Google Resume McDowell | CareerCup.com

3. Slides Posted Online posted at: www.technologywoman.com Click “Speaking Engagements” McDowell | CareerCup.com

4. McDowell | CareerCup.com

5. Interview Process McDowell | CareerCup.com

6. “Elite” Tech Companies Testing aptitude, not knowledge McDowell | CareerCup.com

7. Start-Ups • Coding + Intelligence • “Hit the ground running” • Do you know “their” technologies? • Entrepreneurial • Have you started things? • How much direction do you need? • Personality • Will you fit with the team? but… it varies! McDowell | CareerCup.com

8. PM Roles • Communication Skills • User-Focused Thinking • Passion for Technology • Analytical Skills • Technical Skills (position dependent) McDowell | CareerCup.com

9. How You Are Judged How did you do RELATIVE to other candidates on the SAME question? It’s not about how quickly you solved the problem… … it’s about how quickly you solved it relative to other candidates. McDowell | CareerCup.com

10. Resumes & Application Process McDowell | CareerCup.com

11. How to Get an Interview • Your “Pedigree” • Education • Work Experience • Projects • Github / Online Profile • Make a kick-ass resume McDowell | CareerCup.com

12. How We Review Resumes • Pull resume out of giant stack • Spot-check: company names, positions, projects, schools. • Skim bullets to see if you’ve written real code. “Glanced at,” not read. 15 – 30 seconds Reject Interview • Go to next resume & whine about how many more you have left. McDowell | CareerCup.com

13. How CS Resume Should Look Observe: No Objective! Objectives / summaries are almost always useless. One Page Only! Unless > 10 years exp. A Real Resume Format with organized columns Short (1 – 2 line bullets) Focus on Accomplishments not responsibilities GPAif at least 3.0 max (in-major, overall) 3 – 4 Projects Courses & independent Finished or unfinished List of Technical Skills Short! Cut the “fluff.”

14. Talking to Recruiters • Show: • What you’ve done (mobile app? Show it!) • What you’re excited about • Have a “pitch” ready • Weird is okay • (arrogant is not) McDowell | CareerCup.com

15. Behavioral Questions McDowell | CareerCup.com

16. Communication Goals • Answer the question. • Deliver a *good* answer. • Communicate well. McDowell | CareerCup.com

17. Preparing for Behavioral Qs • Create Preparation Grid for Projects + Behavioral Grid [for PM & less tech. roles] McDowell | CareerCup.com

18. Structure 1: Nugget First • Lead with your “thesis” / nugget • Grabs the listener’s attention • Gives them context for where you’re going. Q: What accomplishment are you most proud of? A: I’m most proud of the way I re-architected the … McDowell | CareerCup.com

19. Structure 2: S.A.R. ituation ction esult S What was the issue? A What did you do about it? R What was the impact? McDowell | CareerCup.com

20. Technical SkillsInterview Prep McDowell | CareerCup.com

21. How to study • Study the basics • Complex algorithms generally unnecessary. • Practice solving questions • Don’t memorize! • See: CtCI & CareerCup.com • Push yourself! • Write code on paper McDowell | CareerCup.com

22. Data Structures • How to implement • When to use (pros / cons) McDowell | CareerCup.com

23. Algorithms • Implementation • Space vs. Time Complexity McDowell | CareerCup.com

24. Concepts • Not just a concept – know how to code! McDowell | CareerCup.com

25. How to Learn CS Fundamentals? • Necessary for “elite” tech companies • Not necessarily otherwise (check interview questions) • MIT Open Courseware • Freshman / sophomore level DS & Algo courses • Books • CLRS (Algorithms) • Online tutorials • Practice implementing and using McDowell | CareerCup.com

26. Technical SkillsMastering the Interview McDowell | CareerCup.com

27. Types of “Serious” Questions • Product Design Questions • Estimation Questions • Software Engineering Questions • Coding & Algorithms • Object Oriented Design • Scalability • Factual / Trivia / Language-Based McDowell | CareerCup.com

28. Product Design Questions How would you design an calculator for the blind? Design an elevator for a building. Pick a Google product. How would you improve it?

29. Product Design Questions: Why? • Communication & Structured Thinking • Ability to understand the user • Creativity • Business instincts / skills

30. Product Design Qs: Approach • Ask questions to resolve ambiguity • Understand the user • Structure the problem • Solve piece by piece

31. Product Design Qs: Example How would you design a calculator for the blind? Step 1: Ask Questions • Adults? Children? Professionals? • Where are they using it? • School, work, etc.

32. Product Design Qs: Example How would you design a calculator for the blind? Step 2: Understand the User • What’s important to a blind child? • Keeping up with the rest of the class • Not feeling “different” • Efficient input / output • What about teachers, parents, classmates, etc.?

33. Product Design Qs: Example How would you design a calculator for the blind? Step 3: Structure • Find a structure • Otherwise, you’re just blabbering • One approach: • Make list of functions necessary • Discuss how to do input / output • Usability for non-blind • Summary

34. Product Design Qs: Example How would you design a calculator for the blind? Step 4: Solve!

35. Estimation Questions How many tennis balls can fit in an SUV? How much money does Gmail make from ads every year? How much do New Yorkers spend on electricity each year?

36. Estimation Qs: Why? • Problem Solving • Basic Quantitative Skills

37. Estimation Qs: How to Approach • Ask questions to resolve ambiguity • Don’t make assumptions (yet) • Outline / Structure Your Approach • Break down the components • Assume numbers when necessary • State assumptions explicitly • Round numbers to make your math easier • Sanity Check • Do your numbers make sense?

38. Estimation Qs: Example How much money does Gmail make from ads every year? Step 1: Ambiguous Information • Profit or revenue? • Past year? Or average over history? • Gmail only? Or include Google Apps?

39. Estimation Qs: Example How much money does Gmail make from ads every year? Step 2: Outline Your Approach (# of users) x (# clicks / year) x ( $ / click )

40. Estimation Qs: Example How much money does Gmail make from ads every year? Step 3: Break down components Estimate # of Gmail users in the US • Assume 300 million people in the US. • Exclude 0 - 12 years old and 65 - 75 years old •  ~ 200 million • Assume 80% of people use email • 80% of those have non-work account … and so on …

41. Estimation Qs: Example How much money does Gmail make from ads every year? Step 4: Validate Numbers • Could revenue be $5 billion? • No, because… • Google’s annual revenue is ~$40 billion • $16 / US citizen (not just Gmail users)

42. How to Solve Tough Problems • Ask Questions! • Questions are more ambiguous than they appear • Talk out loud • Show us how you think • Think critically • Does your algorithm really work? What’s the space and time complexity? • Code slowly and methodically • It’s not a race • Test your code • And make CAREFUL fixes. McDowell | CareerCup.com

43. What does a “good coder” do? • Code in top-left of whiteboard • Pseudocodefirst (if necessary) • Be methodical. Don’t try to rush. • Reasonably Bug Free • Thorough testing (and careful fixing) • Check for error conditions • Clean coding • Use other functions • Good use of data structures (define own if useful) • Concise and readable McDowell | CareerCup.com

44. Types of Interview Questions McDowell | CareerCup.com

45. Algorithm Qs: Pattern Matching Q: Write code to reverse the order of words in a sentence. “dogs are cute” “cute are dogs” Similar to: reverse characters in a string. “dogs are cute” “etuc era sgod” A: Reverse full string, then reverse each word. McDowell | CareerCup.com

46. Algorithm Qs: Simplify & Generalize Q: Design algorithm to figure out if you can build a ransom note (array of strings) from a magazine (array of strings). Simplify: what if we used characters instead of strings?  Build array of character frequencies. Generalize: how we can extend answer to words? A: Build hashtable from word to frequency. McDowell | CareerCup.com

47. Algorithm Qs: Base Case & Build Q: Design algorithm to print subsets of set. {a, b, c}  {}, {a}, {b}, {c}, {a, b}, {a, c}, {b, c}, {a, b, c} S({}) {} S({a}) {}, {a} S({a, b}) {}, {a}, {b}, {a, b} S({a, b, c})  ? A: Build S(n) by cloning S(n-1) and adding n to the cloned sets. McDowell | CareerCup.com

48. Algorithm Qs: Data Structure Brainstorm Q: There are 10^10 possible phone #s. Explain how you could efficiently implement assignSpecificNum(num)and assignAnyAvailableNum(). Array (sorted)? Too slow to remove num. Linked list? Too slow to find specific num. Hash table? Can’t iterate through free nums. Tree? Ah-ha! A: Store free #s in BST. Remove when taken. McDowell | CareerCup.com

49. How To Solve Algorithm Questions Compare to similar problems. Solve first for a simplified / tweaked problem. Solve for n = 1, and build solution for n = 2. Try to apply data structure to solve problem. McDowell | CareerCup.com

50. Whew! All Done! <Gulp> This is a lot of stuff. Do I need to get everything right? McDowell | CareerCup.com