Rotate Image + Word Search

Watch someone solve the problem: rotate image + word search problem in an interview with a FAANG engineer and see the feedback their interviewer left them. Explore this problem and others in our library of interview replays.

Interview Summary

Problem type
The Problem: Rotate Image + Word Search

Interview question
Two medium-difficulty problems are covered back to back. The first asks the interviewee to rotate an N×N matrix 90 degrees clockwise in place, using only O(1) extra space by cycling groups of four elements. The second asks whether a given word can be found in an M×N character grid by traversing sequentially adjacent cells (up, down, left, right) without reusing any cell - a classic backtracking DFS problem with pruning considerations.

Interview Feedback

Feedback about Sergeant Chaos (the interviewee)

Advance this person to the next round?
Yes

How were their technical skills?
4/4

How was their problem-solving ability?
4/4

What about their communication ability?
4/4

Strengths and What Went Well
Demonstrated a structured approach by first breaking down the problem and analyzing how individual cell values change during the transformation.
Communicated clearly throughout the interview and effectively explained the thought process behind the proposed solutions.
Was receptive to feedback and incorporated suggestions well during the discussion.
Successfully solved both problems within the allotted time and validated the solutions against relevant edge cases.

Areas for Improvement
The main area for improvement was the initial explanation of the time complexity for the second problem. However, the candidate recognized the issue and was able to correct the analysis later in the discussion.

Advice for Future Interviews
Continue practicing more challenging coding problems to further strengthen problem-solving skills and prepare for higher-difficulty interview questions.
Pay close attention to accurately analyzing and communicating time and space complexity after arriving at a solution.

Feedback about Verdant Goblin (the interviewer)

Would you want to work with this person?
Yes

How excited would you be to work with them?
3/4

How good were the questions?
3/4

How helpful was your interviewer in guiding you to the solution(s)?
3/4

Interviewer is able to explain the problem clearly. I personally did not have much difficulties solving the problem, but the interviewer is nice and talked to me about things that I'm unclear with. Interviewer was engaged in the whole process, and feedback is simple and understandable. No hints were given since I didn't need them.

Interview Transcript

Sergeant Chaos: Hello
Verdant Goblin: All right, how are you today?

Sergeant Chaos: Uh, yeah, great. I have an interview to start in like, uh, 2 hours, so I hope I can gain some confidence.

Verdant Goblin: Oh, 2 hours? Okay. Um, is there any specific companies or startups or, uh, you know What you're trying to—

Sergeant Chaos: Uh, I think the company would be [REDACTED], but I actually applied in China, so they have a different interview style. I previously failed an [REDACTED] technical interview, so I just want to get myself practice. Okay. Because in my opinion, it seems like the problem is simply implementation, but probably I was not communicating well enough.

Verdant Goblin: Yeah, yeah. So how many years of experience and what role are you applying for so that I can, uh, design my questions accordingly?

Sergeant Chaos: Oh, okay. Um, oh, it depends. Um, I'm currently, um, studying at my university. I have done an internship already. I'm looking for my next internship. Um, but I have participated in the ICPC for some time. Okay. So I do have some basic understanding of the algorithm and stuff.

Verdant Goblin: Okay. All right, then let's get started. What's your language of choice? Is it C++, right? Is that?

Sergeant Chaos: Yes. Yes.

Verdant Goblin: Okay, then we can get started. Any questions before we start? Any— I'm pretty sure that you know this pattern, how this works, and is there anything you want me to clarify before we start?

Sergeant Chaos: Let me think. I cannot think of any questions for now. I think I can just ask for clarification in the interview, right?

Verdant Goblin: Yeah, you can ask me at any time.

Sergeant Chaos: Oh yeah, there's something that comes to my head. So for the feedback, would it be like immediate feedback or you will reply like within some time? First time doing the interview, yeah.

Verdant Goblin: I think since we are doing in another 2 hours, I can provide the short summarized feedback at the end of this interview, maybe 5 minutes, last 5 minutes we can keep it. And then I'll try to submit maybe another 30 minutes or something. I'll try to submit it as soon as possible.

Sergeant Chaos: Okay, thank you so much. So yeah, let's get started, I think.

Verdant Goblin: All right, all right. I'm going to paste my question here.

Sergeant Chaos: Sure. Oh, okay. Let me just— yeah, please allow me some time to read the question. Rotate at 90 degrees. Okay, rotated in place. That's interesting. Okay, so, um, the first idea that comes to my mind is that, as it said, each image will need to be rotated 90 degrees. So there will be, um, there will be 4 numbers that correspond to each other, right? Like in this case, 1 will be rotated to the place of 3, 3 to 9, 9 to 7, and 7 to 1.

Verdant Goblin: Mm-hmm.

Sergeant Chaos: So in theory, we can— in this case, we only need to do that for 1, 4, and 5, which 5 will not get rotated. And for each of the 1 and 4, we find the 4 corresponding ones, which in this case is 1, 3, 9, and 7. And we can rotate these 4 with only 1 additional space. And then we can do this for all the rest.

Verdant Goblin: Okay.

Sergeant Chaos: Do you think that is clear or anything I need to elaborate on?

Verdant Goblin: Um, I think it's pretty clear. Yes, we can go on. What, what would be the time complexity and space complexity for the solution?

Sergeant Chaos: Oh, for this one? Yeah, space complexity, I would say O. Yeah, like, because there will be only one additional space to be allocated. And the space— the time complexity would definitely be O because you definitely need to visit all the pixels, like all the numbers in the matrix. And I don't think you can really avoid that. Yeah, yeah.

Verdant Goblin: Okay, sounds good.

Sergeant Chaos: Okay.

Verdant Goblin: Yeah.

Sergeant Chaos: So yeah, I'll get to implementation.

Verdant Goblin: Yes, yes, go ahead.

The full implementation and detailed analysis can be found throughout the interview transcript, including code snippets and discussions on algorithm design.

Conclusion

The interview covered both the matrix rotation problem and the word search problem, providing a comprehensive view of the interviewee's thought process and technical skills.