Google Intern Software Engineer Interview Experience — 10-Minute Resume Grill, Then First Missing Positive in O(1) Space

The interview started right on time and went straight into an intense 10-minute resume grill. The interviewer homed in on my recent backend work, specifically asking detailed questions about the Kafka streaming architecture and Redis caching implementations from my previous internship in the Platform Cloud org. They also dug into the technical trade-offs I made when building Bastion, focusing heavily on why I chose Go and how I managed latency in a distributed edge API gateway.

Once the background deep dive concluded, the remaining time was dedicated to the coding round. I was asked to solve First Missing Positive (LeetCode 41).

• Initial Approach: I proposed a hash set solution to achieve O(N) time complexity, but the interviewer quickly asked me to optimize the space complexity to O(1).
• Optimal Solution: I pivoted to the cyclic sort method — swapping each valid number x to its corresponding index x - 1.
• Implementation & Edge Cases: I coded the solution in Python and proactively handled out-of-bounds numbers, negatives, and duplicate values to prevent infinite swapping loops.
• Wrap-up: I spent the final few minutes doing a dry run with edge cases provided by the interviewer, followed by a brief Q&A about their team.