Ch9.15: Using Container Ranges with Algorithms

Overview

All fast_io containers provide begin() and end() iterators, which means they work with the C++ standard library algorithms via <algorithm> and <ranges>.

1. Using std::ranges with fast_io Containers

#include <fast_io_dsal/vector.h>
#include <algorithm>
#include <ranges>
#include <fast_io.h>

int main() {
    ::fast_io::vector<::std::size_t> v{5zu, 3zu, 1zu, 4zu, 2zu};

    // Sort using std::ranges
    ::std::ranges::sort(v);
    // v is now {1zu, 2zu, 3zu, 4zu, 5zu}

    // Find an element
    auto it = ::std::ranges::find(v, 3zu);
    if (it != v.end()) {
        ::fast_io::io::println("Found 3 at index ",
            static_cast<::std::size_t>(it - v.begin()));
    }

    // Count elements greater than 2
    auto count = ::std::ranges::count_if(v, [](::std::size_t x) { return x > 2zu; });
    ::fast_io::io::println("Count > 2: ", count); // 3

    // Erase-remove idiom
    ::fast_io::vector<::std::size_t> w{1zu, 2zu, 3zu, 2zu, 4zu, 2zu, 5zu};
    auto new_end = ::std::ranges::remove(w, 2zu);
    w.erase(new_end, w.end());
    // w is now {1zu, 3zu, 4zu, 5zu}
}

2. Free Functions: erase() and erase_if()

You can also use the free functions erase() and erase_if() that are provided for all containers:

::fast_io::vector<::std::size_t> v{1zu, 2zu, 3zu, 2zu, 4zu, 2zu, 5zu};

// Remove all 2s
auto removed = erase(v, 2zu);
// v is now {1zu, 3zu, 4zu, 5zu}, removed == 3

// Remove elements matching a predicate
auto removed2 = erase_if(v, [](::std::size_t x) { return x > 3zu; });
// v is now {1zu, 3zu}, removed2 == 2

Key takeaways

• All fast_io containers work with std::ranges:: algorithms.
• The free functions erase() and erase_if() are provided for all containers.
• std::ranges::sort, std::ranges::find, std::ranges::count_if all work directly.
• The erase-remove idiom works with std::ranges::remove followed by erase().