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c++subsetset-intersection

How do I check if one vector is a subset of another?

Currently, I think my best option is to use std::set_intersection, and then check if the size of the smaller input is the same as the number of elements filled by set_intersection.

Is there a better solution?

Solution

  • Try this:

    if (std::includes(set_one.begin(), set_one.end(),
                  set_two.begin(), set_two.end()))
{
// ...
}

    About includes().

    The includes() algorithm compares two sorted sequences and returns true if every element in the range [start2, finish2) is contained in the range [start1, finish1). It returns false otherwise. includes() assumes that the sequences are sorted using operator<(), or using the predicate comp.

    runs in

    At most ((finish1 - start1) + (finish2 - start2)) * 2 - 1 comparisons are performed.

    Plus O(nlog(n)) for sorting vectors. You won't get it any faster than that.