set

Header: <set>

The <set> header in C++ provides the std::set container, which is an associative container that stores unique elements in a specific sorted order. It is part of the C++ Standard Template Library (STL).

Key Characteristics

• Stores unique elements
• Elements are sorted automatically (default is ascending order)
• Implemented as a balanced binary search tree (usually a red-black tree)
• Provides logarithmic time complexity for insertion, deletion, and search operations
• Does not allow modification of elements directly (elements are const)
• Allows for efficient lookup, insertion, and deletion of elements

Key Components

1. std::set: The main container class for storing unique sorted elements
2. std::multiset: Similar to set, but allows duplicate elements

Example 1: Basic Usage of set

#include <iostream>
#include <set>

int main() {
    std::set<int> numbers = {5, 2, 8, 1, 9};

    numbers.insert(3);
    numbers.insert(1); // Duplicate, won't be inserted

    for (const auto& num : numbers) {
        std::cout << num << " ";
    }
    std::cout << std::endl;

    return 0;
}

Explanation

• Demonstrates creation and initialization of a set
• Shows insertion of elements (including a duplicate)
• Illustrates automatic sorting of elements

Example 2: Set Operations

#include <iostream>
#include <set>

int main() {
    std::set<int> set1 = {1, 2, 3, 4, 5};
    std::set<int> set2 = {4, 5, 6, 7, 8};

    // Find element
    auto it = set1.find(3);
    if (it != set1.end()) {
        std::cout << "Found: " << *it << std::endl;
    }

    // Erase element
    set1.erase(4);

    // Check if element exists
    if (set1.count(4) == 0) {
        std::cout << "4 is not in the set" << std::endl;
    }

    return 0;
}

Explanation

• Shows how to find an element in a set
• Demonstrates erasing an element
• Illustrates checking for the existence of an element

Example 3: Custom Comparator

#include <iostream>
#include <set>
#include <string>

struct CompareLength {
    bool operator()(const std::string& lhs, const std::string& rhs) const {
        return lhs.length() < rhs.length();
    }
};

int main() {
    std::set<std::string, CompareLength> words = {"apple", "banana", "cherry", "date"};

    for (const auto& word : words) {
        std::cout << word << " ";
    }
    std::cout << std::endl;

    return 0;
}

Explanation

• Demonstrates using a custom comparator to sort elements
• Shows how to create a set of strings sorted by length

Additional Considerations

• set is less efficient than unordered_set for simple storage and retrieval, but maintains a sorted order
• Iterators to set elements remain valid after insertion or removal of other elements
• The lower_bound(), upper_bound(), and equal_range() functions can be used for efficient range queries
• set is particularly useful when you need to maintain a sorted collection of unique elements

Summary

The <set> header in C++ provides the std::set container, which is ideal for storing unique elements in a sorted order. It offers logarithmic time complexity for most operations and is implemented as a balanced binary search tree.

Key points to remember:

1. Elements in a set are unique and sorted
2. Provides efficient insertion, deletion, and search operations
3. Does not allow direct modification of elements once inserted
4. Can use custom comparators for sorting
5. Useful for maintaining sorted collections of unique elements

By leveraging std::set, C++ developers can efficiently manage collections of unique elements that need to be kept in a sorted order, making it valuable for tasks such as maintaining a sorted list of unique identifiers or implementing algorithms that require quick lookups in a sorted collection.

Citations:

[1] https://www.geeksforgeeks.org/set-in-cpp-stl/ [2] https://www.tutorialspoint.com/cpp_standard_library/set.htm [3] https://stackoverflow.com/questions/63050845/using-set-in-c-standard-template-library-stl [4] https://en.wikipedia.org/wiki/C%2B%2B_standard_library [5] https://cplusplus.com/reference/set/set/ [6] https://learn.microsoft.com/en-us/cpp/standard-library/basic-ofstream-class?view=msvc-170 [7] https://www.machinet.net/tutorial-eng/common-pitfalls-with-cpp-fstream-and-how-to-avoid-them [8] https://stackoverflow.com/questions/72999240/initializing-stdofstream-object-in-header-file-v-s-source-file