# 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](/content/questions/confusing-number/index.html)

### 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.