Cracking the Coding Interview

Presentation given at University of Waterloo to help students prepare, know what to expect and perform well on coding interviews at the top technology companies

Transcript

1. Cracking the Coding Interview by Marcelo Cortes
2. I am Marcelo…
3. I am Marcelo… Interviewing since 2002
4. I am Marcelo… Interviewing since 2002
5. I am Marcelo… Interviewing since 2002
6. I am Marcelo… Interviewing since 2002
7. I am Marcelo… Interviewing since 2002
8. I am Marcelo… Interviewing since 2002
9. Interview Types
10. Interview Types Coding
11. Interview Types Coding Algorithms
12. Interview Types Coding Algorithms System Design
13. Interview Types Coding Algorithms System Design Selling
14. Interview Types Coding Algorithms System Design Selling
15. The Environment
16. - Phone The Environment
17. - Phone - Video conference The Environment
18. - Phone - Video conference - Onsite with remote interviewer The Environment
19. - Phone - Video conference - Onsite with remote interviewer - Onsite on the whiteboard The Environment
20. - Phone - Video conference - Onsite with remote interviewer - Onsite on the whiteboard - Onsite pair programming The Environment
21. The Interviewer POV
22. - They are very busy but must stop “working” to interview you! The Interviewer POV
23. - They are very busy but must stop “working” to interview you! - They are not there to fail you. They need and want more teammates. They want you to pass! The Interviewer POV
24. - They are very busy but must stop “working” to interview you! - They are not there to fail you. They need and want more teammates. They want you to pass! - They want to enjoy the interview. Have good discussions, maybe learn something new, maybe teach you something. The Interviewer POV
25. Most importantly! They must answer the question: The Interviewer POV
26. Most importantly! They must answer the question: Do I want this person on my team? The Interviewer POV
27. What are they looking for?
28. - Can you communicate your ideas? What are they looking for?
29. - Can you communicate your ideas? - How well do you know the programming language? What are they looking for?
30. - Can you communicate your ideas? - How well do you know the programming language? - Are you coachable? What are they looking for?
31. - Can you communicate your ideas? - How well do you know the programming language? - Are you coachable? - How familiar and efficient are you with the tools? What are they looking for?
32. - Can you communicate your ideas? - How well do you know the programming language? - Are you coachable? - How familiar and efficient are you with the tools? - Do you know algorithms? What are they looking for?
33. - Can you communicate your ideas? - How well do you know the programming language? - Are you coachable? - How familiar and efficient are you with the tools? - Do you know algorithms? - Can you code? Recursion? Iteration? Data structures? What are they looking for?
34. - Can you communicate your ideas? - How well do you know the programming language? - Are you coachable? - How familiar and efficient are you with the tools? - Do you know algorithms? - Can you code? Recursion? Iteration? Data structures? - Code style? Naming? Strategy? What are they looking for?
35. Coding Interview Structure
36. Coding Interview Structure 60 minutes
37. 60 minutes 00..02: Quick intro and get setup Coding Interview Structure
38. 60 minutes 00..02: Quick intro and get setup 02..05: Describing the coding problem Coding Interview Structure
39. 60 minutes 00..02: Quick intro and get setup 02..05: Describing the coding problem 05..15: Discussing algorithm and possible solutions Coding Interview Structure
40. 60 minutes 00..02: Quick intro and get setup 02..05: Describing the coding problem 05..15: Discussing algorithm and possible solutions 15..55: Coding the solution Coding Interview Structure
41. 60 minutes 00..02: Quick intro and get setup 02..05: Describing the coding problem 05..15: Discussing algorithm and possible solutions 15..55: Coding the solution 55..60: Candidate’s turn to ask questions Coding Interview Structure
42. A Simple Problem
43. Given a list of words, find the maximum common prefix between any 2 words in the input list A Simple Problem
44. words = [ ‘electronics’, ‘compact disc’, ‘alphabet’, ‘compass’, ‘giraffe’, ‘electricity’] prefix = ‘electr’ Example
45. - What is the alphabet? Lowercase a to z? ASCII? Unicode? - Do we expect the input to be very large? - Do we expect average string length to be large? - What if there is a tie? - Is null or empty input expected? Questions to Ask
46. The Algorithm Is there an obvious brute force (inefficient) solution?
47. The Algorithm Is there an obvious brute force (inefficient) solution? YES!
48. The Algorithm Is there an obvious brute force (inefficient) solution? YES! Mention it and quickly explain how the algorithm works.
49. Is there an obvious brute force (inefficient) solution? YES! Mention it and quickly explain how the algorithm works. “We can compare each word to every other word and keep track of the largest common prefix found and its length” The Algorithm
50. - Almost always the answer is YES! - Best way to get good at algorithms is practicing! - Always ask questions such as: - Sorting the input helps? - What data structures could help? - Set? Hashmap? Tree? - Can I collect data to help in a first pass? Can we do better?
51. METHOD NAME: findMaxCommonPrefix INPUT: array of strings OUTPUT: string In Java: String findMaxPrefix(List<String> words){…} Define the Interface
52. void validate(String[] words, String expected) { String prefix = findMaxPrefix(words); if (!expected.equals(prefix)) { throw new AssertionError( String.format("Wrong result for %s. “ + “Expected `%s` vs `%s` actual", Arrays.toString(words), expected, prefix)); } } String findMaxPrefix(String[] words) {...} Validation Framework
53. Write Simple Test Cases public static void main(String[] args) { validate(new String[] {"electronics", "compact disc", "alphabet", "compass", "giraffe", "electricity"}, "electr"); validate(new String[] {"electronics"}, ""); validate(new String[] {"electronics", "electronicz"}, "electronic"); validate(new String[] {}, ""); System.out.println("All tests passed!"); }
54. public static void main(String[] args) { validate(new String[] {"electronics", "compact disc", "alphabet", "compass", "giraffe", "electricity"}, "electr"); validate(new String[] {"electronics"}, ""); validate(new String[] {"electronics", "electronicz"}, "electronic"); validate(new String[] {}, ""); System.out.println("All tests passed!"); } All tests passed! Write Simple Test Cases
55. https://goo.gl/vMMjr3 Full Source Code
56. public static String findMaxPrefixBruteForce(String[] words) { String maxPrefix = ""; for (int i = 0; i < words.length; i++) { for (int j = 0; j < words.length; j++) { if (i == j) continue; String commonPrefix = maxCommonPrefix(words[i], words[j]); if (commonPrefix.length() > maxPrefix.length()) { maxPrefix = commonPrefix; } } } return maxPrefix; } private static String maxCommonPrefix(String left, String right) {..} Brute Force
57. private static String maxCommonPrefix(String left, String right) { StringBuilder resultBuilder = new StringBuilder(); for (int i = 0; i < left.length() && i < right.length(); i++) { if (left.charAt(i) != right.charAt(i)) break; resultBuilder.append(left.charAt(i)); } return resultBuilder.toString(); } Brute Force
58. public static String findMaxPrefixHashmap(String[] words) { String maxPrefix = ""; Map<String, Integer> allPrefixes = new LinkedHashMap<>(); for (int i = 0; i < words.length; i++) { String word = words[i]; StringBuilder prefixBuilder = new StringBuilder(); for (int j = 0; j < word.length(); j++) { // Store the prefix and count. See next } } return maxPrefix; } Using Hashmap
59. .. for (int j = 0; j < word.length(); j++) { prefixBuilder.append(word.charAt(j)); String prefix = prefixBuilder.toString(); Integer count = allPrefixes.get(prefix); if (count == null) { allPrefixes.put(prefix, 1); } else { count++; if (maxPrefix.length() < prefix.length()) { maxPrefix = prefix; } } } .. Using Hashmap
60. public static String findMaxPrefixTree(String[] words) { String maxPrefix = ""; TreeNode root = new TreeNode(); for (int i = 0; i < words.length; i++) { TreeNode current = root; boolean matching = true; String word = words[i]; StringBuilder prefixBuilder = new StringBuilder(); for (int j = 0; j < word.length(); j++) { // Add each word to the tree keeping track of max prefix. (See next) } } return maxPrefix; } Using Trie (prefix tree)
61. .. for (int j = 0; j < word.length(); j++) { Character letter = word.charAt(j); TreeNode child = current.children.get(letter); if (child != null) { if (matching) { prefixBuilder.append(letter); if (prefixBuilder.length() > maxPrefix.length()) { maxPrefix = prefixBuilder.toString(); } } } else { matching = false; child = new TreeNode(); current.children.put(letter, child); } current = child; } .. Using Trie (prefix tree continuation...)
62. Don’t ask: - How you did in the interview, your solution, other solutions - Better ways to solve the problem. - Salary, Bonus, Options, Etc. Do ask: - About the company, team, the product, the job - The tools, the work environment, the mission - How the team prioritize tasks, etc Your turn to ask questions
63. Conclusion
64. - Practice a lot! Be prepared! That’s the best way to be calm and perform well. Conclusion
65. - Practice a lot! Be prepared! That’s the best way to be calm and perform well. - Arrive early. Have your environment ready. Do not waste time on setup, that will take time away from your interview. Conclusion
66. - Practice a lot! Be prepared! That’s the best way to be calm and perform well. - Arrive early. Have your environment ready. Do not waste time on setup, that will take time away from your interview. - Communicate well and often. Ask questions. Keep talking. Conclusion
67. - Practice a lot! Be prepared! That’s the best way to be calm and perform well. - Arrive early. Have your environment ready. Do not waste time on setup, that will take time away from your interview. - Communicate well and often. Ask questions. Keep talking. - Have a strategy. Discuss options. If stuck, ask for advice. Conclusion
68. - Practice a lot! Be prepared! That’s the best way to be calm and perform well. - Arrive early. Have your environment ready. Do not waste time on setup, that will take time away from your interview. - Communicate well and often. Ask questions. Keep talking. - Have a strategy. Discuss options. If stuck, ask for advice. - Make sure you understand the problem. Write a simple test framework. Start with a test case. Conclusion
69. - Practice a lot! Be prepared! That’s the best way to be calm and perform well. - Arrive early. Have your environment ready. Do not waste time on setup, that will take time away from your interview. - Communicate well and often. Ask questions. Keep talking. - Have a strategy. Discuss options. If stuck, ask for advice. - Make sure you understand the problem. Write a simple test framework. Start with a test case. HAVE FUN! Conclusion
70. I’d love to hear from you! marcelo@indigofair.com @mescortes Q&A