SweatyImposterSenior track

Senior

Full senior loop prep. All patterns, hard problems, the complete SD bank, every production technique and tradeoff, and behavioral that probes leadership, judgment, and strategic thinking.

Overall progress

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Be able to triage AND solve from every pattern.

Browse all patterns

The hardest in the bank — interview-grade for senior loops.

Minimum Window Substring

hard · blind75

First Missing Positive

Reverse Nodes in k-Group

Find Median from Data Stream

hard · blind75

Sliding Window Median

Merge k Sorted Lists

hard · blind75

Smallest Range Covering K Lists

Alien Dictionary

hard · blind75

Largest Rectangle in Histogram

All 10 canonical prompts including the long tail.

Browse all prompts

Backoff, idempotency, hedged requests, leases, quorum — the senior-engineer toolbox.

Browse all techniques

Including the deeper ones like 2PC vs Saga, multi-leader replication.

Browse all tradeoffs

Leadership without authority, conflict, strategic thinking, hiring, hard feedback.

Tell me about a time you strongly disagreed with a peer's technical decision. How did you handle it?

Conflict & Influence

Describe a time you disagreed with your manager. What did you do?

Conflict & Influence

Tell me about a technical decision you made that turned out to be wrong. What was the impact and what did you learn?

Failure & Ownership

Describe how you've helped a junior or struggling engineer grow.

Leadership & Mentorship

Tell me about a time you led a project where you had no direct authority over the contributors.

Leadership & Mentorship

Tell me about a time you had to cut scope to hit a deadline.

Prioritization & Tradeoffs

Describe a time you had to decide between rewriting a system and improving it incrementally.

Technical Judgment

Tell me about a time you said no to a significant request from leadership or a major stakeholder.

Prioritization & Tradeoffs

Walk me through a production incident you led the response to.

Crisis & Operations

Tell me about a multi-quarter technical vision or architecture you drove. What was the long view?

Strategic Thinking

Tell me about a hire you advocated for who didn't work out, or one you opposed who did.

Describe a time you worked closely with an underperforming engineer (peer or report). What happened?

Describe a time a security review or compliance requirement forced you to change a design late.

Cross-Functional Collaboration

Tell me about a time you gave someone difficult feedback. How did they receive it?

Growth & Feedback

Tell me about a piece of feedback you received that was hard to hear. What did you do with it?

Growth & Feedback

Tell me about a time you had to say 'I don't know' in a high-stakes setting.

Race conditions, TOCTOU, timing attacks, hidden O(n²), cache invalidation — the bugs that ship to prod.

Practice code review

This endpoint serves fine under low load but tail latency explodes under concurrency. Why?

Wrong async · python

What is the most serious correctness issue (assume userPath is already validated to be a safe filename)?

Time-of-check-time-of-use · java

An attacker can crash this worker with a single small request. What's the issue?

Unbounded recursion · python

What's the subtle bug in reapExpired?

Mutable shared state · typescript

main prints true — but a similar-looking input prints false. Where's the bug?

Floating point · java

What's the security flaw here?

Auth bypass · java

All challenges, including the subtle ones — reference vs value, type coercion, mutating during iteration.

Practice debugging

isEven(0.5) → expected false, got false

Idempotency-Key, ETag concurrency, 202 + Location for async jobs, webhooks with HMAC, 404 vs 403.

Practice API design

You're building a payments API (Application Programming Interface). Clients sometimes retry after a timeout and you cannot double-charge. Pick the best endpoint for creating a charge.

A post on your social app can have millions of comments and the feed appends new ones constantly. The mobile client needs to scroll through them. Pick the best endpoint.

Long-running operations

Customers can request a CSV export of all their orders. Generating it takes 30 seconds to 10 minutes. Pick the best endpoint design.

Bulk operations

Your warehouse system needs to update on-hand counts for up to 5,000 SKUs at once after a nightly stock count. Pick the best endpoint.

Users upload videos up to 5 GB to your platform. Pick the best endpoint design for the upload path.

Concurrency control

Two editors open the same document and both save changes a few seconds apart. You need to detect and reject the second save instead of silently overwriting the first. Pick the best endpoint.

Error responses

An authenticated user requests GET /v1/documents/{id}, but that document belongs to a different tenant and they have no permission to see it. Pick the best response.

Your platform sends webhook events to subscribers when a payment succeeds. You're designing the outbound HTTP (Hypertext Transfer Protocol) call. Pick the best design.

Recursive CTEs, percentile / median, ranking with ties, EXISTS vs IN NULL traps, pivot.

Ranking with ties

Return the top 2 sales reps in each region by total amount. If two reps tie, both should appear and the next rep should be skipped (classic 1, 2, 2, 4 ranking).

Window function

Return each day with a running total of revenue from the earliest day through that day, ordered by day.

Return the median salary per department in PostgreSQL. Use a continuous median (interpolate between the two middle values for even-sized groups).

Given a CEO with manager_id IS NULL, return every employee in the org along with their depth (CEO = 0, direct reports = 1, etc.).

Return the names of products that have NEVER been returned. The returns table can contain rows with product_id IS NULL.

In PostgreSQL, pivot 2025 orders into one row per region with columns q1, q2, q3, q4 holding the sum of total for that quarter.

Update with JOIN

In PostgreSQL, set status = 'inactive' for every user who has placed no orders in the last 365 days (including users who have NEVER placed an order). Update only users currently not already inactive.

Multi-tenant isolation, crypto choice (AES-GCM vs CBC), OAuth flows, PKCE, cert pinning, brute-force defenses.

Practice security

Users can write comments that other users see. Your template engine inserts the raw string into both an HTML body and a JavaScript onclick attribute. How should you defend against XSS (Cross-Site Scripting)?

You are shipping a banking iOS app that talks to api.bank.example over HTTPS. The threat model includes users on hostile Wi-Fi and the possibility of a compromised public CA. What TLS (Transport Layer Security) posture makes sense?

You need to encrypt small JSON (JavaScript Object Notation) blobs (user notes) at rest in the database. You will manage the keys via KMS. Which symmetric mode should you reach for?

You are integrating Sign in with Google into a public SPA that has no backend it can call its own (the SPA talks directly to your API). Which OAuth flow should the SPA use?

Rate limiting / abuse

Your /login endpoint is getting hammered: credential-stuffing attempts from thousands of residential IPs, sometimes one attempt per IP. You also do not want to lock real users out. What rate-limiting strategy fits?

Multi-tenant isolation

Your SaaS stores all tenants in one Postgres database with a tenant_id column on every table. A new engineer is writing queries and forgets the tenant filter on a JOIN, leaking data across tenants in staging. How do you prevent this systemically?

All 10 prompts. Strategy for pricing, State pattern, hold-on-Show, per-subscriber offsets.

Practice OOP design

Design a chess game: model the board, pieces, legal-move generation, turn order, and game-end detection (checkmate, stalemate, draws). Focus on a piece hierarchy that's easy to extend.

Hotel Reservation System

Design a hotel reservation system that supports searching available rooms by date range and room type, booking with pricing, modifying or cancelling reservations, and check-in/check-out at the property.

Pub/Sub Event System

Design an in-process pub/sub system: publishers post messages to topics, and subscribers receive messages from topics they subscribe to. Support multiple subscribers per topic, retention, and delivery guarantees.

Movie Ticket Booking

Design a movie ticket booking system: theaters with multiple screens, movies showing at scheduled times, seat selection with temporary holds during checkout, and payment that confirms the booking.

Sharding keys, partitioning, hot rows, RLS, denormalize-or-don't — 10 schema prompts.

Practice DB design

Chat / Messaging

Design the schema for a chat product that supports 1:1 and group conversations, persistent message history, per-user read receipts, and presence. Optimize for the dominant read pattern: 'load the last N messages in a conversation, newest first.'

E-commerce Product Catalog

Design the schema for a catalog that supports products with variants (size, color), nested categories, multi-currency pricing, and per-warehouse inventory. Read-heavy: product detail pages and category listings dominate traffic.

Multi-tenant SaaS

Design the schema for a B2B SaaS where every row belongs to a tenant (workspace). Pick an isolation strategy and justify it. The product has users, projects, and tasks; tenants range from 5 to 50,000 seats.

Social Network Feed

Design the schema for a Twitter-like service: users follow other users, post short messages, and like posts. Generate each user's home timeline. Discuss fan-out-on-write versus fan-out-on-read for timeline assembly.

Booking / Reservations

Design the schema for a booking system (hotel rooms, restaurant tables, or meeting rooms — pick one). Holds expire after a TTL (Time-To-Live) if the user does not check out. Prevent any two confirmed bookings from overlapping for the same resource.

Subscription Billing

Design the schema for a SaaS billing system: customers subscribe to plans, get billed on a cycle, and may upgrade / downgrade with proration mid-cycle. Failed payments retry on a schedule. Every monetary movement must be auditable.

Ride-sharing / Geospatial

Design the schema for an Uber-like service: riders request trips, drivers accept them, and the system must find the nearest available drivers to a pickup point in real time. Trip history powers earnings and dispute resolution.

Dijkstra, Bellman-Ford, Floyd-Warshall, MST, max flow, KMP, Aho-Corasick, suffix arrays, Fenwick, LCA.

Practice algorithms

Graph - shortest path

You're routing packets across a peering network where some carriers pay you to take their traffic, so a few links have negative cost. You need the cheapest path and must also flag any negative-cost cycles. What's the right approach?

Graph - shortest path

A logistics planner needs the shortest delivery time between every pair of 400 warehouses, given a dense distance matrix with positive and a handful of negative adjustments. The query needs to answer any pair instantly afterwards. What's the right approach?

A chip designer needs the minimum-cost wiring tree over 2,000 pads where nearly every pair has a candidate route, giving roughly two million edges. Memory is tight and edge sorting would be expensive. What's the right approach?

Graph - max flow

You have 500 interns and 500 projects, with a bipartite graph of who can work on what. You need the largest set of assignments where each intern gets at most one project and each project gets at most one intern. What's the right approach?

You're analyzing a microservice call graph to find groups of services that mutually depend on each other (so you can flag the cyclic clusters). The graph has ~200k nodes and ~1M directed edges. What's the right approach?

An analytics service tracks per-minute revenue and serves two query types: 'add X to minute i' and 'sum of revenue from minute L to minute R'. Both happen millions of times per day over a fixed-size timeline. What's the right approach?

You have a fixed array of one million sensor readings and need to answer 'min reading in [L, R]' for ten million queries. The data never changes after load. What's the right approach?

String - palindromes

You're scanning DNA strings up to 10 million bases and need the longest palindromic substring of each. A naive O(n^2) DP is too slow. What's the right approach?

String matching

A content moderator needs to scan each chat message for any match against a dictionary of 50,000 banned phrases. Messages arrive at high throughput; the dictionary is mostly static. What's the right approach?

Suffix structures

You're comparing five large source files (each ~1MB) and need the longest substring that appears in all of them. A pairwise dynamic programming table would be huge. What's the right approach?

You have a static org-chart tree of 200,000 employees and must answer 'who's the lowest common manager of employees u and v' for a million queries. What's the right approach?

Given a permutation of 2 million user-ranking scores, you need the exact count of inversions (pairs i<j with a[i]>a[j]) to measure how reordered a feed became. An O(n^2) double loop is too slow. What's the right approach?

A streaming pipeline emits log lines forever and you must keep a uniformly random sample of exactly 1,000 lines at any moment, without knowing the total count in advance and without buffering everything. What's the right approach?

Lock-free, memory ordering, CRDTs, vector clocks, chain replication, IO_uring, zero-copy — the deep cuts.

Open Systems quiz

Compare-And-Swap (CAS) / Atomics

Hardware-level atomic instruction: write a new value only if the current value matches expected; otherwise retry.

Immutable / Copy-On-Write

Never mutate a shared object; on write, copy it and atomically swap the reference. Readers are entirely lock-free.

Vector Clocks / Version Vectors

Each replica tags writes with a per-node counter map. Comparing two versions reveals causal order, concurrency, or strict dominance.

Merkle Tree Anti-Entropy

Replicas build a tree of hashes over their key ranges; comparing root then children lets them find divergent ranges in O(log n) hops instead of full scans.

CRDT (Conflict-Free Replicated Data Type)

Data types whose merge function is commutative, associative, and idempotent, so any two replicas converge to the same value without coordination.

If a target replica is down, a healthy node stores the write locally with a 'hint' and forwards it once the target recovers. Keeps write availability high.

Chain Replication

Replicas arranged in a chain: writes enter at the head, flow through every link, commit at the tail. Reads served by tail give linearizable results with simple logic.

Bloom Filter for LSM Negative Lookups

Attach a small probabilistic filter to each SSTable. A point lookup checks the filter first and skips the file if it says 'definitely not present'.

TCP Congestion Control (Reno / Cubic / BBR)

Algorithms that decide how fast TCP (Transmission Control Protocol) sends. Loss-based (Reno, Cubic) treat packet loss as congestion; model-based (BBR) measures bottleneck bandwidth and round-trip time (RTT) directly.

HTTP/3 over QUIC

HTTP (Hypertext Transfer Protocol) 3 runs over QUIC, a UDP (User Datagram Protocol) based transport with built-in TLS (Transport Layer Security) 1.3, per-stream flow control, and connection migration across IP changes.

Event-driven I/O (epoll / kqueue / io_uring)

Readiness-based (epoll, kqueue) or completion-based (io_uring, IOCP) APIs that let one thread watch tens of thousands of file descriptors without a thread per connection.

Zero-copy (sendfile / splice)

Move bytes from disk to socket without copying through user space. The kernel hands page-cache pages directly to the NIC's DMA engine.

The harder calls — mutex vs CAS, shared memory vs messages, leader vs leaderless, quorum vs single-master, HTTP/2 vs HTTP/3.

Guard the counter with a mutex (`ReentrantLock`) vs Use a lock-free `AtomicLong` with CAS

A hot counter is hit by 64 threads thousands of times per second. You need correctness without crush

Shared memory + locks across components vs Actors / message-passing — each component owns its state

You're building a stateful service with many internal components mutating shared state. You want to

Leader-follower (Postgres, MySQL, Raft KV) vs Leaderless (Cassandra, DynamoDB, Riak)

Write-heavy time-series workload, 100k writes/sec, can tolerate eventual reads, must stay available

Quorum writes (W=2) vs Single-master writes

A user-profile service with N=3 replicas per key, light contention, multi-region.

Raft consensus over membership list vs Gossip / SWIM-based membership

Tracking which of ~1500 worker nodes are alive in a batch-processing cluster.

Heap-organized table with separate indexes vs Index-organized table clustered by primary key

Choosing between Postgres-style heap tables and MySQL/InnoDB-style index-organized tables (clustered

HTTP/2 over TCP vs HTTP/3 over QUIC

Serving a global audience over flaky mobile networks. Pick HTTP (Hypertext Transfer Protocol) 2 or H

Allow 0-RTT for resumed sessions vs Require 1-RTT (no early data)

Returning clients are hitting your API (Application Programming Interface). Do you allow TLS (Transp

Buffered I/O (page cache) vs Direct I/O (O_DIRECT)

Database is doing its own page cache and you do not want the kernel double-buffering. Buffered or di

Every question, including the multi-input and amortized cases.

Open Big O Quiz

Run the Senior preset under timer pressure. Identify gaps, drill weakest patterns.

Start a senior mock