I thought of some mixed algorithm: binary + interpolation search. While first has $O(\log n)$ runtime in both worst and average cases, second has $O(n)$ worst case runtime and $O(\log \log n)$ average case.

However, I think, if such algorithms can exist, there are more than one of them.

Anyway, what I want to know if there is any known algorithm with restrictions given in title.

Note. It must be appliable to simple arrays without repeatitions (no precomputing/hashing).


1 Answer 1


Yup. Do interpolation search, but after $\log n$ iterations, if you haven't found the answer yet, switch to binary search. This ensures a $O(\log n)$ worst-case running time, while retaining the $O(\log \log n)$ average-case running time. Note that the average case only applies if you make a particular assumption about the distribution of values in the array.

  • $\begingroup$ Oh, right, how could I miss this trivial solution... $\endgroup$
    – rus9384
    Commented Dec 7, 2017 at 8:41

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