Big O, without the maths
By the end of today you can look at a loop and say how its cost grows as the input grows, explain why that matters more than raw speed, and name the complexity of the operations you use every day.
YesterdayOn Day 5 you measured a list membership check against a set and saw the gap widen with size. Today you get the vocabulary for what you observed.
TomorrowTomorrow you use that vocabulary on arrays and strings, and meet your first algorithm pattern.
Why this matters
Big O is how engineers compare approaches before writing either one. It is also the language of every technical interview, and the reason a database index on Day 43 is worth the write cost.
- Big O
- Time complexity
- Space complexity
- Amortised cost
Learn it
70 minCopy this into Claude or ChatGPT. It quizzes you before it explains anything, which is deliberate. The resources under it are how you check what it told you.
Today's Master Prompt
Free · sign inA prompt written for this day alone: your level, the exact scope, what to leave out, and an instruction to quiz you before it explains anything. Paste it into Claude or ChatGPT and it teaches you today's material.
Check it against something that is not a model
An assistant can be fluent and wrong, and on a topic you met today you will not catch it. These cover the same ground and were made by people who do this for a living, so they are what you hold the explanation up against. They are other people's work and we only link to them, so judge them for yourself.
4 hand-picked resources
Free · sign inVideos, official docs and articles covering the same ground, each opened and annotated by hand. They are what you check the assistant against on a day you cannot yet catch it being wrong.
Build it
40 minWrite four functions over a list: return the first item, sum all items, find duplicates with nested loops, and find duplicates using a set. Time all four at 1,000 and 10,000 items with timeit. Predict the ratio before you measure, then compare your prediction against reality.
Recall it
25 minAnswer out loud, reveal, then mark honestly whether you had it. That score is the only thing on this page you do not get to choose.
5 recall questions
Free · sign inQuestions you answer from memory, then grade yourself against the real answer. The score is carried into the mastery rating below it, so an honest miss cannot quietly become a tick.
Rate it
Completion and mastery are tracked separately. Be honest, because an inflated rating only means the concept resurfaces sooner.
Mastery tracking
Free · sign inRate yourself against five named criteria per concept. Completion and mastery are tracked separately, and anything you rate shakily comes back automatically on a spaced schedule.
Recap
- 01Big O describes growth, not speed
- 02Constants are dropped because they do not change the shape
- 03Space complexity is the trade of memory for work
- 04Measure as well as reason; constant factors are real
Your progress
Free · sign inMark days complete, pick up where you left off across devices, and watch completion and mastery diverge. Free, and the account exists only so ninety days of work cannot vanish with a cleared browser.