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Cracking the Algorithm & Coding Interview

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How to walk through an algorithm & coding interview

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Cracking the Algorithm & Coding Interview

  1. 1. GayleL.McDowell | Founder/ CEO gayle in/gaylemcdgayle Cracking the Algorithm & Coding Interview SVCC SiliconValleyCodeCamp
  2. 2. gayle in/gaylemcdgayleGayle Laakmann McDowell 2 Hi! I’m Gayle LaakmannMcDowell Author Interview Coach Interview Consulting <dev> </dev> (CS) (MBA)
  3. 3. Gayle Laakmann McDowell 3gayle in/gaylemcdgayle Yes! Slidesare online! Gayle.com  Click“Events”  Ctrl-F for “SiliconValley”
  4. 4. But why? Why why why why why why meeeee 01
  5. 5. gayle in/gaylemcdgayle 5 z Gayle Laakmann McDowell What Really Happens
  6. 6. Gayle Laakmann McDowell 6gayle in/gaylemcdgayle Why? Strong CS fundamentals Analytical skills Make tradeoffs Push throughhard problems Communication How you think
  7. 7. Preparation Why why why why why why meeeee 02
  8. 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) Breadth-FirstSearch Recursion Graphs Depth-FirstSearch Memoization/ Dynamic Programming Stacks/ Queues BinarySearch Heaps
  9. 9. gayle in/gaylemcdgayleGayle Laakmann McDowell 9 Preparation ImplementDS/Algorithms MASTER BigO Practice with interviewquestions Code on paper/whiteboard Mock interviews PUSHYOURSELF!
  10. 10. Expectations & Evaluation Why why why why why why meeeee 03
  11. 11. gayle in/gaylemcdgayle 11 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.
  12. 12. gayle in/gaylemcdgayle 12 z Gayle Laakmann McDowell What IS expected Be excitedabout hard problems More thanjust “correct” Drive! Keeptrying when stuck Write real code Showmehowyouthink!
  13. 13. gayle in/gaylemcdgayle 13 z Gayle Laakmann McDowell How You’re Evaluated RELATIVE Not a “metric” / timer Nooneisperfect!
  14. 14. Solving Why why why why why why meeeee 04
  15. 15. gayle in/gaylemcdgayle 15 z Gayle Laakmann McDowell How To Approach CrackingTheCodingInterview.com“Resources”
  16. 16. gayle in/gaylemcdgayle 16Gayle Laakmann McDowell step Listen (for clues)
  17. 17. Gayle Laakmann McDowell 17gayle in/gaylemcdgayle What’sthe clue? Anagram server  Ex: rates ->aster, stare, taser, tears Clue:why is it ona server?
  18. 18. gayle in/gaylemcdgayle 18Gayle Laakmann McDowell step Draw an Example Big Enough General Purpose +
  19. 19. gayle in/gaylemcdgayleGayle Laakmann McDowell 19 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 common element, sameindex
  20. 20. gayle in/gaylemcdgayleGayle Laakmann McDowell 20 Ex:Intersection ofTwo Sorted Arrays Better: [1, 12, 15, 19, 20, 21] [2, 15, 17, 19, 21, 25, 27]  Big  No specialcases
  21. 21. gayle in/gaylemcdgayle 21Gayle Laakmann McDowell step Brute Force / Naive Stupid&terribleisokay!
  22. 22. gayle in/gaylemcdgayle 22Gayle Laakmann McDowell step Optimize Walk through brute force Look for optimizations
  23. 23. Gayle Laakmann McDowell 23gayle in/gaylemcdgayle Techniques to Develop Algorithms Optimize A. BUD B. Space/time C. Doityourself Solve D. Recursion E. Solve “incorrectly” F. Other data structures Pushyourself!
  24. 24. Gayle Laakmann McDowell 24gayle in/gaylemcdgayle (A) Look for BUD Bottlenecks Unnecessary work Duplicated work
  25. 25. Gayle Laakmann McDowell 25gayle in/gaylemcdgayle What’s the bottleneck?  Ex: countingthe intersection [1, 12, 15, 19, 20, 21] [2, 15, 17, 19, 21, 25, 27]  Bottleneck:searching B
  26. 26. Gayle Laakmann McDowell 26gayle in/gaylemcdgayle What’s unnecessary?  Ex: a3 + b3 = c3 + d3 (1 <=a,b, c, d<= 1000  Unnecessary: looking for d U
  27. 27. Gayle Laakmann McDowell 27gayle in/gaylemcdgayle What’s unnecessary?  Ex: a3 + b3 = c3 + d3 (1 <=a,b, c, d<= 1000  Unnecessary: looking for d U
  28. 28. Gayle Laakmann McDowell 28gayle in/gaylemcdgayle What’s duplicated?  Ex: a3 + b3 = c3 + d3 (1 <=a,b, c, d<= 1000  Duplicated: c, d pairs D
  29. 29. Gayle Laakmann McDowell 29gayle in/gaylemcdgayle What’s duplicated?  Ex: a3 + b3 = c3 + d3 (1 <=a,b, c, d<= 1000  Duplicated: c, d pairs D
  30. 30. Gayle Laakmann McDowell 30gayle in/gaylemcdgayle What’s duplicated?  Ex: a3 + b3 = c3 + d3 (1 <=a,b, c, d<= 1000 D
  31. 31. Gayle Laakmann McDowell 31gayle in/gaylemcdgayle What’s duplicated?  Ex: a3 + b3 = c3 + d3 (1 <=a,b, c, d<= 1000 D
  32. 32. Gayle Laakmann McDowell 32gayle in/gaylemcdgayle (B)Space/TimeTradeoffs Hashtables & other datastructures Precomputing
  33. 33. Gayle Laakmann McDowell 33gayle in/gaylemcdgayle Space/Time Tradeoffs Hashtables  Find # pairs withsum INPUT: array = [5, 15, 8, 9, 3, 2, -1, 4] sum = 7 OUTPUT: 3 pairs = (5, 2), (8, -1), (3, 4)  Putitemsinto hashtable
  34. 34. Gayle Laakmann McDowell 34gayle in/gaylemcdgayle Space/Time Tradeoffs  Precomputing  Find rectangle at origin w biggest sum 6 5 -9 2 -2 -5 -2 7 3 -2 10 13 -8 -3 1 -2  Brute force: compute all rectanglesand sums
  35. 35. Gayle Laakmann McDowell 35gayle in/gaylemcdgayle Space/Time Tradeoffs  Precomputing  Find rectangle with biggest sum 6 5 -9 2 -2 -5 -2 7 3 -2 10 13 -8 -3 1 -2 -+ + 10=
  36. 36. Gayle Laakmann McDowell 36gayle in/gaylemcdgayle Space/Time Tradeoffs  Precomputing  Find rectangle with biggest sum 6 5 -9 2 -2 -5 -2 7 3 -2 10 13 -8 -3 1 -2 -+ + 13=
  37. 37. Gayle Laakmann McDowell 37gayle in/gaylemcdgayle (C)Do it yourself Findpermutationsof swithinb  s = abbc  b = babcabbacaabcbabcacbb Findthem!  … now how didyou actuallydoit?
  38. 38. Gayle Laakmann McDowell 38gayle in/gaylemcdgayle Techniques to Develop Algorithms Optimize A. BUD B. Space/time C. Doityourself Solve D. Recursion E. Solve “incorrectly” F. Other data structures Pushyourself!
  39. 39. Gayle Laakmann McDowell 39gayle in/gaylemcdgayle (D) Recursion/ Base Case & Build Subsets of a set  {}  {}  {a}  {}, {a}  {a, b}  {}, {a}, {b}, {a, b}  {a, b, c}  … Subsets of {S1…Sn-1} + Sn to each
  40. 40. Gayle Laakmann McDowell 40gayle in/gaylemcdgayle (E) Solve “incorrectly” ① Develop incorrectsolution ② Identifywhy preciselyit’s incorrect ③ Repair ④ (& Repeat)
  41. 41. Gayle Laakmann McDowell 41gayle in/gaylemcdgayle (E)Solve “incorrectly” Random node in BST Try: flipcoin Coin=Heads  Branch Left Coin=Tails  Branch Right
  42. 42. Gayle Laakmann McDowell 42gayle in/gaylemcdgayle (E)Solve “incorrectly” Random node in BST Try: random number in {0, 1, 2} R=0  Branch Left R=2  Branch Right R=1  Return root
  43. 43. Gayle Laakmann McDowell 43gayle in/gaylemcdgayle (E)Solve “incorrectly” Random node in BST Try:  Return rootwith1/n probability  Then flipcoin(heads left,tails->right)
  44. 44. Gayle Laakmann McDowell 44gayle in/gaylemcdgayle (E)Solve “incorrectly” Random node in BST Try: pick random # 0 throughn-1 R=0  Return root R>left.size  Branch right 1<=R<=left.size  Branch left
  45. 45. Gayle Laakmann McDowell 45gayle in/gaylemcdgayle (F) Other Data Structures Giving outphone numbers  “I wantany availablenumber”  “I wantthisnumber” Try: sorted array?Sorted linkedlist?Hashtable? BST?
  46. 46. gayle in/gaylemcdgayle 46Gayle Laakmann McDowell step Walk Through Know the variables andwhen they change
  47. 47. gayle in/gaylemcdgayle 47Gayle Laakmann McDowell step Write Beautiful Code
  48. 48. Gayle Laakmann McDowell 48gayle in/gaylemcdgayle How to Write WhiteboardCode Modularized Error cases / TODOs Good variables Write straight Top-leftcorner Use arrows if needed Languagechoiceisuptoyou!
  49. 49. gayle in/gaylemcdgayleGayle Laakmann McDowell 49 Modularization
  50. 50. gayle in/gaylemcdgayle 50Gayle Laakmann McDowell step Testing FIRST Analyze  What’sitdoing?Why?  Anythingthatlooksweird?  Errorhotspots THEN use test cases  Smalltestcases  Edgecases  Bigger testcases
  51. 51. Final Thoughts And questions 05
  52. 52. gayle in/gaylemcdgayle 52 z Gayle Laakmann McDowell It’s done for a reason! Be a great teammate. Be a great engineer.
  53. 53. gayle in/gaylemcdgayleGayle Laakmann McDowell 53 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

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