Courses
19 interactive courses and 95 lessons across coding patterns, system design, and behavioral interviews. Visualizations, runnable Python, worked answers, and quizzes. Your first course is free.
Coding patterns
The algorithms behind most whiteboard questions.
Sliding Window
Turn O(n·k) scans into one O(n) pass by reusing the work you already did.
5 lessons · ~50 min
Two Pointers
Two indices, one pass: cut the pair-checking search space without missing an answer.
5 lessons · ~47 min
Binary Search
Every comparison throws away half of what's left. Twenty questions beats a million.
5 lessons · ~49 min
BFS & DFS
Two ways to walk a graph: ripple outward level by level, or dive deep and backtrack.
5 lessons · ~51 min
Hash Maps
Trade a little memory for O(1) answers to "have I seen this before?"
5 lessons · ~47 min
Stacks & Monotonic Stacks
Last in, first out: the right tool whenever the most recent thing matters most.
5 lessons · ~48 min
Heaps & Top-K
Keep the best candidate on top without ever fully sorting.
5 lessons · ~49 min
Backtracking
Try it, undo it, try the next thing: exhaustive search that cleans up after itself.
5 lessons · ~50 min
Dynamic Programming
Solve each subproblem once, write it down, and hard problems collapse into loops.
5 lessons · ~52 min
Then go use it
Learning sticks when it gets used the same day. Each course ends where the real work starts.
Practice the pattern
Real questions that test each pattern, in a code editor with execution and AI feedback.
Open the practice hub →Prove it in an interview
A live voice interviewer, a real editor, and a hire verdict. Every course page has a one-click interview on its concept.
Set up a mock interview →System design
The building blocks every design interview assembles: watch requests flow through the architectures, then run the simulations.
Caching
Answer the repeat questions from memory, and most of your traffic never touches the database.
5 lessons · ~51 min
Load Balancing & Scaling
One server becomes twenty behind a single address, and nobody on the outside can tell.
5 lessons · ~50 min
Database Scaling
Index it, replicate it, then shard it, in that order and only as far as the numbers force you.
5 lessons · ~52 min
Consistency & Trade-offs
When the network splits, you choose what breaks. Know what you're choosing.
5 lessons · ~51 min
Queues & Async Processing
Take the slow work out of the request, promise to do it soon, and smooth every spike.
5 lessons · ~50 min
Then go use it
Every concept here maps onto the design library's problems, and each course can put you straight into a design interview.
Design on the whiteboard
Full design prompts on a canvas with AI feedback, each tagged with the concepts it exercises.
Open the design library →Prove it in an interview
A 45-minute live design interview with follow-up questions and a verdict. One click from any course page.
Set up a design interview →Behavioral
The stories interviews always ask for, and how to tell yours so they land.
Telling the Story
Your experience is the easy part. Getting it across in two minutes is the skill.
5 lessons · ~47 min
Conflict & Disagreement
Every team fights. Interviewers want to know what you're like when yours does.
5 lessons · ~45 min
Failure & Ownership
The failure question isn't about the failure. It's about whether you can be trusted with the next one.
5 lessons · ~45 min
Leadership & Influence
Leading is getting the right thing to happen without waiting to be in charge of it.
5 lessons · ~45 min
Ambiguity & Prioritization
Nobody hands senior engineers clean requirements. These questions check if you need them.
5 lessons · ~45 min
Then go use it
Write or dictate answers to real behavioral questions and get an AI verdict, or take a live behavioral mock.
Practice your answers
Classic behavioral questions with an answer editor, dictation, and AI feedback graded against what interviewers listen for.
Open the question bank →Prove it in an interview
A live behavioral interview with follow-up questions and a verdict, one click from any course page.
Set up a behavioral interview →