To each their own. I find "Hashsets have O(1) amortized lookup and insert performance assuming a relatively uniform hash distribution, otherwise O(n)" a perfectly reasonable explanation even if it is marginally more complex than "Hashsets always have O(1) amortized lookup and insert performance". I doubt that most students would fail to understand the first explanation.
It's also a valuable lesson to students to teach them that you have to specify whether you mean best case, average or worst case performance when analysing algorithms.
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To each their own. I find "Hashsets have O(1) amortized lookup and insert performance assuming a relatively uniform hash distribution, otherwise O(n)" a perfectly reasonable explanation even if it is marginally more complex than "Hashsets always have O(1) amortized lookup and insert performance". I doubt that most students would fail to understand the first explanation.
It's also a valuable lesson to students to teach them that you have to specify whether you mean best case, average or worst case performance when analysing algorithms.