Summary
I had a positive first-round interview at Doppel, which focused on a multi-part problem centered around Conway's Game of Life, testing my implementation, pattern recognition, and system design thinking for an infinite board. The process felt like a great candidate experience, emphasizing fundamentals over typical LeetCode brainteasers.
Full Experience
My first round interview at Doppel, a startup focused on detecting social engineering attacks for brands, involved a comprehensive problem. The core challenge was to implement Conway's Game of Life. It started with a detailed problem description outlining the M x N grid, live/dead cell states ('O' and '.'), and the four rules governing cell interaction with its eight neighbors. I had to implement this logic and simulate it for K generations, printing the board's state after each. Part 2 involved analyzing patterns in new test cases provided by the interviewer, prompting me to use critical thinking to explain why certain patterns emerged. Part 3 pushed the problem further by asking how to simulate an infinite board with finite memory, a classic system design consideration. Finally, Part 4 built on my Part 2 observations, asking how I would optimize the implementation based on the noticed patterns. Overall, Doppel's interview process was exceptional from a candidate's perspective. I felt my skills were genuinely tested without resorting to typical LeetCode brainteasers. The questions focused on fundamentals and critical thinking, which I found much more engaging and relevant than other interview styles. This particular question was well-suited to gauge a candidate's level and fostered a meaningful, collaborative discussion with the interviewer.
Interview Questions (1)
A board is made up of an M x N grid of cells, where each cell has an initial state:
- live (represented by a letter “O”), or
- dead (represented by a dot “.”).
Each cell interacts with its eight neighbors (horizontal, vertical, diagonal) using the following four rules:
- Any live cell with fewer than two live neighbors dies as if caused by under-population.
- Any live cell with two or three live neighbors lives on to the next generation.
- Any live cell with more than three live neighbors dies, as if by overpopulation.
- Any dead cell with exactly three live neighbors becomes a live cell, as if by reproduction.
The next state is created by applying the above rules simultaneously to every cell in the current state, where births and deaths occur simultaneously.
Part 1: Implement the game
Implement the above logic and print the state of the board after each generation. You need to be able to run the simulation for K generations. A sample test case was provided by the interviewer.
Part 2: Do you notice any patterns in the new test cases?
The interviewer provided some sample starting boards of their choice and asked me to run the state of the board. I was asked to identify any patterns noticed and explain why that pattern makes sense, encouraging me to use critical thinking.
Part 3: Infinite board
Considering the code written, which assumed a finite board, I was asked how I would simulate an infinite grid with finite memory if we wanted to run this code in such a scenario.
Part 4: Continuation of Part 2
Based on what I answered in Part 2 regarding patterns, I was then asked how I would optimize the implementation.