JavaScript Interview with a FAANG engineer

Interview Summary

Problem type
Confusable number
Interview question
Consider an auction: there are BIDDERS in the audience. Each BIDDER is given a paddle with a unique number (e.g.: 57). At the front, there is an ORGANIZER. When a BIDDER raises their paddle, the ORGANIZER sees it and recognizes the number. For instance, a BIDDER might raise paddle #78, and the ORGANIZER recognizes the number 78.

Sometimes, however, a BIDDER accidentally holds the paddle upside down. For instance, a BIDDER with the number 68 holds it upside down, showing the number 89. The ORGANIZER assumes it's 89, which is a mistake. We'll call any number that--when turned upside down--is a different, valid number, a CONFUSABLE number.

Write a function that, given a room with 800 BIDDERS, identifies all the confusable numbers.

Read more about the questions

• Confusing Number

Interview Feedback

Feedback about Fresh Bear (the interviewee)
Advance this person to the next round? No
How were their technical skills? 3/4
How was their problem solving ability? 3/4
What about their communication ability? 3/4

Pros:

• Good job making an assumption that the bidders go from 1 to 800
• Good job talking through the problem statement
• Good job deciding that 1 is reversible
• Good job focusing on digits up front
• Good job thinking out loud
• Good job clarifying about input/output parameters
• Good job identifying leading zero edge case
• Good job thinking through more use cases after we clarified about the definition of confusable number
• Good job using examples to help understand the problem space
• Good job asking about whether we should pursue a more performant solution

Things to think about:

• Missed digit '0', but you did remember to add it later
• If your question is "this seems simple; am I missing something?", the answer is probably "yes"
• Write down your assumptions (e.g.: number-with-2345-inverted-is-by-definition-not-confusable)
• When listing confusables between 1 - 20, you missed 18. I wonder if there's an opportunity to improve thoroughness?

Things to improve:

• Missed the part of the confusable number definition (must be different number)
• Initial implementation of isCharsConfusable is incorrect (includes 9).
• Missed the upside-down-is-same case

Verdict: Strong no hire. Didn't think through test cases thoroughly, and the solution is incomplete.
Recommendations:

• Understand the stages: requirements refinement, algorithm definition, algorithm implementation
• Improve requirements refinement: identify MORE test cases

Feedback about Sly Chinchilla (the interviewer)
Would you want to work with this person? Yes
How excited would you be to work with them? 4/4
How good were the questions? 4/4
How helpful was your interviewer in guiding you to the solution(s)? 4/4

Interview Transcript

Sly Chinchilla: Hello, hello, hello.
Fresh Bear: Hey, how are you doing?
Sly Chinchilla: I'm great. Can you hear me okay?
Fresh Bear: Yeah, can you hear me okay?
Sly Chinchilla: Absolutely. This is, um, this is a rare event that both of us have a working AV setup right out of the gate. Wow, that's awesome.
Fresh Bear: Yeah, they don't have a setup mode. So that's probably why people mess up.

Followed by the discussion of the interview structure and problem exploration.

Examined Test Cases and Edge Cases

• Clarification on the ability to identify confusable numbers.
• Step through various numbers, analyzing their potential confusability.
• Communication among analogs such as 1, 6, 8, 9 and identification of implications of either lowercase or flipped representations.

Conclusion and Key Observations

• Detailed discussion indicating the need for structured exploration of algorithms.
• Importance of acknowledging distinctive aspects of test cases and assumptions while iterating through solutions.