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I was asked the O() of binary search. I said "log n". They asked "what base?"

... obviously they wanted 2, but O() doesn't work that way - changing base is a constant factor. Sometimes there's a tension between figuring out someone's understanding of the algorithm and someone's understanding of the notation (and math behind it). Of course, I gave them both answers...




> changing base is a constant factor.

Only if the base is constant. For example B-trees have O(log_B n)-time operations, and you can't ignore the B because it is a parameter (hence non-constant).

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What was the second answer?

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2 and the "no need for base in big-O" makes 2 :).

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Maybe they wanted both answers?

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