What's the Most Efficient Method for Removing Duplicates and Sorting a C Vector?

Most Efficient Way to Erase Duplicates and Sort a Vector

To efficiently erase duplicates and sort a C vector, consider the approach of sorting and then using the std::unique function. However, there's a potential flaw in the code you provided: the unique function modifies the order of elements, which can disrupt the sorted order.

Additionally, the order of operations can impact performance. If the vector contains many duplicates, erasing them first (using unique) may be more efficient. However, if the duplicates are evenly distributed, sorting first may be faster.

A more efficient alternative is to convert the vector into a std::set using a set constructor:

set<int> s(vec.begin(), vec.end());
vec.assign(s.begin(), s.end());

This approach guarantees uniqueness and correct sorting because it utilizes the natural properties of a set. As the provided benchmark shows, when the number of duplicates is large enough, converting to a set and back is faster than directly manipulating the vector.

Finally, it's worth noting that manually converting to a set (e.g., set s; for (unsigned i = 0; i < size; i) s.insert(vec[i]);) can be slightly faster than using the set constructor on small datasets. However, for large vectors, the set constructor becomes more efficient.

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