Google Interview Guide

Google is the most algorithm-purist of the big five, and the single most useful thing to internalise is that the first solution is the entry fee, not the answer. The interview is the ladder of follow-ups that comes after it — tighten the constraint, remove the extra space, make it work on a stream — and your score is decided by how you handle rungs three and four.

The second thing to internalise is structural: your interviewer does not hire you. An independent hiring committee that never met you reads their notes. Anything you thought but did not say does not exist.

Crowd-reported, not published

No company publishes its question bank. The round structure and the bar below are corroborated by recruiters and candidates; the problem list is crowd-reported, stale, and biased toward whoever posted it. Treat the pattern families as the durable signal — which families a company leans on changes far more slowly than which individual problems it uses.

The most algorithm-purist of the big five. Expect a clean problem, then layers of follow-ups that keep tightening the constraints until you are designing rather than recalling.

The loop

Phone screen 1× · 45 min One medium, coded in a shared doc or CoderPad

Onsite coding 2-3× · 45 min Medium to hard, heavy on follow-up laddering

Googlyness & leadership 1× · 45 min Behavioural, collaboration, ambiguity

System design 1× · 45 min L5 and above only

The bar

Scores are on a 1-4 scale per interviewer and go to an independent hiring committee that never met you — so your interviewer's notes are the only evidence. Narrate constantly; unexplained correct code scores worse than explained near-miss code.

What they lean on

This is the durable part. Which pattern families a company favours is far more stable than which individual problems it uses, so prepare in this order:

1. graph-traversal-and-connected-components
2. binary-search-on-answer
3. two-dimensional-dp-and-knapsack
4. tries
5. sliding-window
6. monotonic-stack
7. shortest-paths-dijkstra-bellman-ford-and-floyd-warshall

Quirks worth knowing

• The follow-up ladder is the real interview. Getting the first solution fast buys you harder questions, not an early finish.
• Complexity analysis is graded explicitly. State time and space before you are asked, every time.
• Expect "now make it O(1) space" or "now the input is a stream" on almost every problem.
• Hiring committee review means the process is slow. Weeks between onsite and offer is normal, not a bad sign.

Reported problems

Read this before you trust the list. No company publishes its question bank. Every "asked at Google" list in circulation — including this one — is aggregated from candidate reports, is months to years out of date, and over-represents whoever bothered to post. Use it to choose an order to practise in. Do not use it as a question bank, and do not assume a problem missing from it is safe to skip.

27 problems

2 easy15 medium10 hard

AllEasyMediumHard

Unsolved onlyExportImportReset

• ○1Two SumeasyNeetCode 150Blind 75LeetCode Top Interview 150
• ○20Valid ParentheseseasyNeetCode 150Blind 75LeetCode Top Interview 150
• ○3Longest Substring Without Repeating CharactersmediumNeetCode 150Blind 75LeetCode Top Interview 150
• ○56Merge IntervalsmediumNeetCode 150Blind 75LeetCode Top Interview 150
• ○146LRU CachemediumNeetCode 150LeetCode Top Interview 150
• ○200Number of IslandsmediumNeetCode 150Blind 75LeetCode Top Interview 150
• ○72Edit DistancemediumNeetCode 150LeetCode Top Interview 150
• ○139Word BreakmediumNeetCode 150Blind 75LeetCode Top Interview 150
• ○207Course SchedulemediumNeetCode 150Blind 75LeetCode Top Interview 150
• ○300Longest Increasing SubsequencemediumNeetCode 150Blind 75LeetCode Top Interview 150
• ○322Coin ChangemediumNeetCode 150Blind 75LeetCode Top Interview 150
• ○1143Longest Common SubsequencemediumNeetCode 150
• ○133Clone GraphmediumNeetCode 150Blind 75LeetCode Top Interview 150
• ○208Implement Trie (Prefix Tree)mediumNeetCode 150Blind 75LeetCode Top Interview 150
• ○743Network Delay TimemediumNeetCode 150
• ○787Cheapest Flights Within K StopsmediumNeetCode 150
• ○875Koko Eating BananasmediumNeetCode 150
• ○4Median of Two Sorted ArrayshardNeetCode 150LeetCode Top Interview 150
• ○42Trapping Rain WaterhardNeetCode 150LeetCode Top Interview 150
• ○76Minimum Window SubstringhardNeetCode 150Blind 75LeetCode Top Interview 150
• ○295Find Median from Data StreamhardNeetCode 150Blind 75LeetCode Top Interview 150
• ○297Serialize and Deserialize Binary TreehardNeetCode 150Blind 75
• ○84Largest Rectangle in HistogramhardNeetCode 150
• ○127Word LadderhardNeetCode 150LeetCode Top Interview 150
• ○212Word Search IIhardNeetCode 150Blind 75LeetCode Top Interview 150
• ○239Sliding Window MaximumhardNeetCode 150
• ○269Alien DictionarypremiumhardNeetCode 150Blind 75

Pitfalls

• Solving it silently. The hiring committee reads notes, not your code. Unexplained correct code scores below explained near-miss code, because the notes cannot record reasoning you never voiced.
• Treating the first solution as the finish line. Expect two to four follow-ups per problem. Budget time for them: a polished optimal solution with no time left for follow-ups scores worse than a good solution plus two rungs climbed.
• Skipping the brute force because you recognised the pattern. Recognition is exactly what makes you vulnerable here — the follow-up ladder often starts by breaking the assumption your pattern relied on.
• Not asking about constraints. Google interviewers frequently leave them out deliberately, and the missing constraint is usually the hinge of the whole problem.

Interview follow-ups

They ask	What they’re checking	The answer
“Now do it in $O(1)$ space.”	Whether your solution’s space is incidental or understood	Name what the extra space is for. If it is a hash map for lookups, the answer is usually sort-plus-two-pointers; if it is a recursion stack, an explicit stack or Morris-style traversal.
“The input is now a stream you cannot store.”	Whether your state is bounded	Say what state you must keep and whether it is bounded. A running max or a size-$k$ heap survives; anything needing a sort or random access does not.
“What if the values can be negative?”	Whether you checked your invariant	The classic window-breaker. If your approach assumed a monotonic running sum, say so and switch to prefix sums plus a hash map.
“Scale it to a thousand machines.”	Whether you can leave the single-machine frame	Partition by key, compute locally, merge. Name the shuffle as the expensive step. This is where the L5+ system design round starts leaking into the coding round.

Recall card

• The follow-up ladder is the interview. Budget time for rungs three and four; the first solution is the entry fee.
• A hiring committee that never met you reads the notes. Narrate everything — unvoiced reasoning does not exist.
• Ask for the constraints. They are often withheld on purpose, and the missing one is usually the hinge.
• Expect the space follow-up. Know the $O(1)$-space variant of every pattern you claim.
• State the brute force even when you recognise the pattern — the ladder often begins by breaking your assumption.