A Set (which we will implement as an unordered_set) is similar to an unordered_map, but instead of storing key-value pairs, they store only the keys.

An unordered_set ensures that every element is distinct, meaning duplicates aren't permitted.

They're part of the C++ Standard Library and are invaluable for tasks like isolating unique items from a collection.

Here's an example of how we can use unordered_set:

#include <iostream>
#include <unordered_set>

using namespace std;

int main() {
    // Create a set
    unordered_set<int> mySet = {1, 2, 3, 4, 5};

    // Add elements to the set
    mySet.insert(6);
    mySet.insert(7);

    // Remove an element from the set
    mySet.erase(2);

    // Checking if an element is in a set
    if (mySet.find(10) != mySet.end()) {
        cout << "Found 10 in mySet" << endl;
    }

    // Check size of the set
    cout << "Size of mySet: " << mySet.size() << endl;

    // Check if a set is empty
    if (mySet.empty()) {
        cout << "Set is empty!" << endl;
    } else {
        cout << "Set is not empty!" << endl;
    }

    // Clearing all elements from a set
    mySet.clear();
    cout << "After clearing, size: " << mySet.size() << endl;
}

You can learn more about C++ unordered_set by clicking here.

Now let's look at some common coding interview questions that use sets!