Big-O Cheat Sheet
One page with the time and space complexity of every common data structure operation and sorting algorithm, colour coded so the expensive cases are obvious. The single most reused reference in interview preparation.
Cheat sheet
Interview Prep
Eric Rowell
Ongoing reference
All
Free
What it is
A single page holding the average and worst case complexities for array, list, hash table, tree and heap operations, plus the sorting algorithms, plus a chart of how the complexity classes diverge as input grows.
Why keep it open while practising
Complexity is the follow up question to almost every coding answer, and hesitating on it undoes the impression a correct solution just made. Checking against this page after each practice problem, until you stop needing to, is about the cheapest preparation available.
The part people overlook
The graph at the top. Seeing how sharply quadratic separates from linearithmic at realistic input sizes is what makes the difference feel real rather than notational, which is what you need when you are justifying a choice out loud.
Best for: everyone, permanently. Bookmark it and use it during practice, not the night before.
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