techmore.in

C++ Sets

In C++, sets are associative containers that store unique elements following a specific order. The std::set is part of the Standard Template Library (STL) and is typically implemented as a balanced binary search tree (often a Red-Black Tree). Here’s a breakdown of how to use std::set:

Basic Operations with std::set

  1. Include the Necessary Header:

    cpp
    #include 
#include

  2. Declare a Set:

    cpp
    std::set<int> mySet;

    By default, std::set stores elements in ascending order. You can also specify a custom comparator to change the order.

  3. Add Elements:

    cpp
    mySet.insert(5);
mySet.insert(10);
mySet.insert(3);

    Note: std::set automatically ignores duplicate elements. If you try to insert an element that already exists, it will not be added again.

  4. Check for Presence of an Element:

    cpp
    if (mySet.find(10) != mySet.end()) {
    std::cout << "10 is in the set." << std::endl;
}

  5. Remove Elements:

    cpp
    mySet.erase(5);  // Removes the element with value 5

  6. Iterate Through the Set:

    cpp
    for (const auto& elem : mySet) {
    std::cout << elem << " ";
}
std::cout << std::endl;

  7. Get the Size of the Set:

    cpp
    std::cout << "Size of the set: " << mySet.size() << std::endl;

  8. Check if the Set is Empty:

    cpp
    if (mySet.empty()) {
    std::cout << "Set is empty." << std::endl;
}

Custom Comparator

If you want to store elements in a custom order, you can provide a comparator:

  1. Define a Custom Comparator:

    cpp
    struct Compare {
    bool operator()(int a, int b) const {
        return a > b;  // Descending order
    }
};

  2. Declare a Set with the Custom Comparator:

    cpp
    std::set<int, Compare> customSet;

Example Code

Here's a complete example illustrating basic operations and a custom comparator:

cpp
#include 
#include 

// Custom comparator for descending order
struct Compare {
    bool operator()(int a, int b) const {
        return a > b;  // Descending order
    }
};

int main() {
    // Default set (ascending order)
    std::set<int> mySet = {5, 10, 3, 7, 7};

    std::cout << "Default set:" << std::endl;
    for (const auto& elem : mySet) {
        std::cout << elem << " ";
    }
    std::cout << std::endl;

    // Set with custom comparator (descending order)
    std::set<int, Compare> customSet = {5, 10, 3, 7};

    std::cout << "Custom set (descending order):" << std::endl;
    for (const auto& elem : customSet) {
        std::cout << elem << " ";
    }
    std::cout << std::endl;

    // Check presence and remove elements
    if (mySet.find(10) != mySet.end()) {
        std::cout << "10 is in the default set." << std::endl;
    }

    mySet.erase(10);

    std::cout << "After removing 10, default set:" << std::endl;
    for (const auto& elem : mySet) {
        std::cout << elem << " ";
    }
    std::cout << std::endl;

    return 0;
}

Output

vbnet
Default set:
3 5 7 10
Custom set (descending order):
10 7 5 3
10 is in the default set.
After removing 10, default set:
3 5 7

This example demonstrates the basic usage of std::set, including iteration, custom ordering, and element management.