Every deck

Each deck has its own page with the questions and answers written out — readable without JavaScript, and a decent way to skim before drilling.

System design

• CAP, PACELC and consistency models16What the theorem actually says, the half of PACELC everyone forgets, and the difference between the consistency guarantees people name and the ones they mean.
• Replication and partitioning17Leaders, followers and quorums; range, hash and directory partitioning; and the hot key that no partitioning scheme splits.
• Caching strategies16Hit ratio as a curve, invalidation as the real problem, and the three write strategies with what each one loses.
• Queueing, latency and backpressure16Little’s Law, the utilisation curve, what a queue is really for, and why the tail is the only percentile that matters at scale.
• Consensus and coordination16Quorums, leader election, distributed locks that cannot guarantee mutual exclusion, and what a clock cannot tell you.
• Failure modes and the patterns that contain them16Retry storms, circuit breakers, bulkheads, timeout budgets and the metastable failures that outlast their own cause.
• Asynchronous messaging and delivery guarantees16At-least-once as a guarantee rather than a defect, the dual-write problem, ordering against parallelism, and exactly-once effect.
• Observability, security and cost17The three questions an interviewer asks after the design is drawn, and the ones candidates most often have no answer for.

Cross-cutting algorithms

• Big-O reasoning and amortized analysis19Deriving bounds rather than reciting them: where the log comes from, what amortized actually promises, and when the constant factor decides.
• Which algorithm does this problem want?18Pattern recognition from problem statements — the skill an interview actually tests before you write a line.
• Space and time trade-offs17What you buy with an extra array, when memoization pays, and when the answer is to spend time instead.
• Recursion and the call stack17Frames, depth, tail calls and the conversion to iteration — plus what actually overflows and when.
• When sorting first is worth it18The n log n tax and the problems it makes trivial — and the ones where it is strictly wasted work.
• Graph representation choices18Adjacency list versus matrix versus edge list, judged by the operation you perform most.
• Stability, in-place, and when they matter18Two properties that sound academic until a multi-key sort or a memory limit makes them the whole question.
• Common interview follow-up chains18Answer, then "what if it is weighted?", then "what if it does not fit in memory?" — rehearsing the escalation.

By algorithm

• Merge sort16
• Quicksort14
• Binary search17
• Two pointers17
• Sliding window18
• Breadth-first search18
• Depth-first search17
• Dijkstra's algorithm18
• Topological sort18
• Union–Find17
• BST insertion14
• BST search14
• Memoization (Fibonacci)17
• Heap operations15
• Coin change17
• 0/1 knapsack15
• Longest increasing subsequence14
• Edit distance16