Google interview questions for engineering roles

Reported interview periodJan 2026

Compressed Vector Dot Product

Design a compact representation for an integer vector that contains long runs of repeated values, then compute the dot product of two vectors stored in that representation without expanding either vector.

Practice focusUse run-length encoding: each vector is a sequence of (value, run length) pairs. Implement: The two vectors must describe the same logical length. Return 0 for two empty vectors and raise ValueError when their expanded lengths differ. Run lengths are positive integers. Your solution should run in O(len(a) + len(b)) time and use O(1) auxiliary space beyond iterator state. Staged follow-ups 1. Explain when run-length encoding is preferable to a sparse (index, value) representation. 2.…