DeepSeek AI & ML Engineer interview questions

MoE is why some frontier models have huge parameter counts but serve cheaply. The signal is the sparse-activation idea, the routing mechanism, and the operational cost (memory, load balancing) that the FLOP savings quietly hide.

RL alignment moved from PPO to leaner methods, and DeepSeek-R1 made GRPO famous. The signal is knowing what the value/critic model does in PPO and how GRPO replaces it. Here is the mechanism, not the acronyms.

Reasoning models are the 2025-2026 frontier. The signal is knowing they are trained (largely via RL on verifiable rewards) to produce long internal reasoning, and that they scale on a second axis: spending more compute at inference.

MQA and GQA shrink the KV cache by sharing key/value heads. MLA takes a different route: compress K and V into a low-rank latent and cache that. The signal is knowing it is a cache trick, not a head-sharing trick, and why it keeps quality.

MoE saves compute but is awkward to serve: experts must be sharded, tokens routed across devices, and batches balanced. The signal is the all-to-all communication and the load-imbalance problem, not the training story.

Almost everyone can quote softmax(QKᵀ/√d_k)V. The interviewer wants the variance argument and the exact training failure the scale prevents. Here is the answer that separates memorization from understanding.

The single most-asked applied GenAI question, and the one most candidates answer as a definition dump. The interviewer wants a decision framework with a default and the conditions that flip it. Here is the call that scores.

A favorite practical screen at the labs, because it tests concurrency, time handling, and judgment in 20 lines. The trap is the background thread that wastes CPU. Here is the lazy-refill version interviewers want, plus the follow-ups.

These are the knobs every LLM product tunes, and the interviewer wants to know what each does to the probability distribution and which setting fits which task. Including why factual and creative tasks want opposite settings.

A classic that tests whether you reach past sorting for the right structure. The signal is the heap solution (O(n log k)), the bucket-sort O(n) trick, and how it changes for an unbounded stream. Here is the answer.

Alignment is now table stakes even outside 'safety' roles. The interviewer wants the three-stage RLHF pipeline and a crisp account of why DPO dropped the reward model entirely. Here is the answer with the mechanism, not the buzzwords.

Tokenization looks like plumbing until it explains your bill, your latency, and why the model fumbles numbers and rare languages. The signal is knowing how subword tokenizers work and the consequences that fall out of them.

The canonical grid DP where each cell depends on three neighbors at once. The signal interviewers want is the min-of-three recurrence, and the reason it has to be min. Here is the answer.

A sudden 22-point AUC jump is a gift and a warning. Junior candidates celebrate; strong ones get suspicious and know exactly which leakage checks to run before anything ships.

Evaluation is the hardest, most underrated part of shipping LLMs. The signal is knowing why public benchmarks mislead, why LLM-as-judge is biased, and how to build a task-specific eval you actually trust.

Offline metrics gate releases; online metrics tell you what actually happened with users. The signal is knowing why offline wins routinely fail to hold online, and how the two feed each other.

Autocomplete is the canonical trie question, and it tests whether you reach for the right structure instead of scanning a word list. The signal is O(prefix) lookup, the DFS to collect completions, and the follow-ups (ranking, memory). Here is the build.

Sliding window is one of the highest-yield coding patterns, and this is its canonical problem. The real signal is recognizing when a window collapses an O(n squared) scan into one linear pass, and maintaining the invariant cleanly.

Graph traversal underpins a huge class of interview problems. The signal is knowing the BFS-vs-DFS tradeoff (shortest path vs memory shape) and applying it cleanly, then handling the directed-vs-undirected cycle gotcha most candidates miss.

A common ML-coding check that verifies you actually understand the metrics you quote. The signal is getting TP/FP/FN/TN right and knowing macro vs micro averaging for multiclass, not reaching for sklearn.

Bit-manipulation problems screen for comfort with binary and the O(1)-space tricks most candidates fumble. The tell is whether you reach for XOR's self-canceling property and the n & (n-1) idiom on instinct. Here is the toolkit.