Java Interview with a FAANG engineer

Interview Summary

Problem type
Number of Unique Islands

Interview question
Given: A 2D array of integers representing land and water.
Values of 0 represent water. Values of 1 are land.
An "island" is a set of adjacent (N, S, E, or W) values = 1.
Your task: count the number of unique island shapes.

For example:

[[1, 1, 0, 0, 0, 0, 0],  
 [1, 0, 0, 0, 1, 1, 0],  
 [1, 0, 0, 0, 0, 1, 0],  
 [0, 0, 1, 1, 0, 0, 0],  
 [0, 0, 1, 0, 0, 1, 1],  
 [0, 0, 1, 0, 0, 1, 0]]  

There are four islands.
The islands in the top left, and bottom 3rd column are the same shape.

Interview Feedback

Feedback about Hyper Bandit (the interviewee)
Advance this person to the next round?
Yes

How were their technical skills?
3/4
How was their problem solving ability?
3/4
What about their communication ability?
2/4

Great interview. Good intuition and approach. Some prompting required to head in the right direction.

What went well:

• good questions to scope the question (minimum size, rows the same width) for your solution
• great initial approach for the easier part of the question
• good intuition for solving the second part of the question and good initial solution with a little prompting
• good problem-solving when confronted with edge case scenario

Room for improvement:

• variable and method naming. Single-letter variable names should be reserved for simple loops where you don't need the value out of that context, or for meanings that are obvious (l = length, w = width was fine, r for row and c for column would have been better than i, j) and "helper" methods should say what they are doing.
• some moments of silence as you thought, hard for me to know what you were thinking
• parameter mutability. Understand when you can/can't modify it.

Feedback about Metal Taco (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

Metal Taco: Hello. How are you doing?
Hyper Bandit: Good, how are you doing?
Metal Taco: Fantastic, thank you. A pleasure to virtually meet you. Looks like we have a standard algorithmic interview for today.
Hyper Bandit: Okay.
Metal Taco: Alright, your lucky question today's...

Hyper Bandit: I'm thinking of doing it by going through the 2D array and once I meet a one, I will use a helper function...

Metal Taco: That sounds like a good approach to start with.

Key Concepts

• An island is defined by contiguous 1s in the matrix.
• The task involves identifying unique shapes by their relative positioning.
• It's important to communicate during problem solving to help the interviewer follow your thought process.
• Efficient data structures like hash sets may be useful for tracking unique shapes.