How do I use sets in C++ STL?

How do I use sets in C++ STL?

In C++, you can use the set container from the Standard Template Library (STL) to store unique elements. Here's a basic example:

#include <iostream>
#include <set>

int main() {
    std::set<int> mySet;
    mySet.insert(1);
    mySet.insert(2);
    mySet.insert(2); // Duplicate, won't be added

    for (int x : mySet) {
        std::cout << x << " ";
    }
    return 0;
}

This will output 1 2.

What are the advantages of using sets over vectors?

Sets automatically handle duplicates and keep elements sorted, which can be beneficial for certain operations like searching. Vectors, on the other hand, allow for faster access by index but do not enforce uniqueness.

Can I perform operations like union and intersection with sets?

Yes, you can perform union and intersection operations using the std::set_union and std::set_intersection algorithms from the <algorithm> header. Here's a quick example for union:

#include <algorithm>
#include <set>
#include <vector>

std::set<int> setA = {1, 2, 3};
std::set<int> setB = {3, 4, 5};
std::vector<int> result;

std::set_union(setA.begin(), setA.end(), setB.begin(), setB.end(), std::back_inserter(result));

This will give you a vector containing the union of both sets.

Are there any performance considerations I should be aware of?

Yes, sets are typically implemented as balanced binary trees, which means operations like insertion, deletion, and lookup have a logarithmic time complexity. If you need faster access and don't require sorted order or uniqueness, consider using a std::unordered_set, which offers average constant time complexity for these operations.