Coding interview questions keep coming back to a small set of patterns, system designs reuse the same building blocks, and behavioral rounds circle a few themes. These free guides cover 16 coding patterns, 6 system design building blocks and 6 behavioral themes, in the order to learn them. Each one explains when it applies and how to talk it through, lists practice questions from Devana's question bank, and ends with a 15-minute prove-it mock interview.
How each guide works
- Read the explainer. When the pattern applies, the idea behind it, a Python template for the coding patterns, the time and space it costs, common mistakes and how to explain it out loud.
- Practice on real questions. Each guide lists 3 to 6 questions from Devana's bank. Each one starts a voice mock interview on that question, so you practice saying your approach as well as finding it.
- Prove it. A 15-minute mock interview on a question that is not on the practice list. Score 70 or more out of 100 and the topic is marked proven.
- Track it. Signed in, the Roadmap view in the Question bank shows every topic as not started, practicing or proven.
Coding patterns
Sixteen patterns in the order to learn them, from arrays and hashing to bit manipulation. Practice them in coding mock interviews.
Foundations
- Arrays and hashingTrade memory for speed: answer each question about the past with a constant-time lookup.
- Two pointersWalk two indexes through the data so each step rules something out.
- Sliding windowKeep a contiguous range and update it as one element enters and one leaves.
- StackKeep the most recent unfinished item on top; pop it when its answer arrives.
Searching and linking
Trees and priority
Exploring options
Optimization
System design building blocks
Six pieces most designs are built from, and how to talk through each one. Practice them in system design mock interviews.
- Requirements and estimationAgree what to build and how big, then turn the scale into a few numbers.
- Load balancing and stateless servicesSpread requests across identical servers that keep no state of their own.
- CachingKeep copies close to where they are read, and decide how stale they may be.
- Choosing and modeling a databaseStart from the queries that must be fast, then choose tables, keys and indexes.
- Sharding and replicationCopy data for reads and safety; split it so writes and size can grow.
- Message queues and async workHand slow or bursty work to a queue, and make consumers safe to run twice.
Behavioral themes
The STAR method, then five themes interviewers come back to. Practice them in behavioral mock interviews.
- The STAR methodSituation, task, action, result: the order that answers what the interviewer needs to know.
- Conflict and disagreementDisagree on substance, keep the relationship, and commit once it is decided.
- OwnershipShow a time you took responsibility beyond the minimum and saw it through.
- Failure and mistakesPick a real failure, own your part, and show what you do differently now.
- Leadership and influenceShow how you moved people without authority: evidence, listening, small wins.
- Ambiguity and changing prioritiesShow how you turned an unclear goal into a plan and kept people informed.
Where to start
- New to coding interviews. Go in order from arrays and hashing. Later patterns build on the earlier ones.
- Interview in a week or two. Prove the foundations first, then practice on your target company's question set in the Question bank.
- Senior or backend role. Start the system design track early. Requirements and estimation comes first because every design answer starts there.
- Behavioral round coming up. Read the STAR method, then prepare one story per theme and tell each one out loud before the day.