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:heavy_check_mark: verify/graph/library_checker_maximum_independent_set.test.cpp

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Code

#define PROBLEM "https://judge.yosupo.jp/problem/maximum_independent_set"

#include "../../utilities/fast_io.hpp"

#include <bits/stdc++.h>
using namespace std;

#include "../../graph/graph.hpp"
#include "../../graph/maximum_clique.hpp"

int main() {
    m1une::utilities::FastInput fast_input;
    m1une::utilities::FastOutput fast_output;

    int N, M;
    fast_input >> N >> M;
    m1une::graph::Graph<> g(N);
    while (M--) {
        int u, v;
        fast_input >> u >> v;
        g.add_edge(u, v);
    }
    auto independent = m1une::graph::maximum_independent_set(g);
    fast_output << independent.size() << '\n';
    for (int x : independent.vertices) {
        fast_output << x << ' ';
    }
    fast_output << '\n';
}
#line 1 "verify/graph/library_checker_maximum_independent_set.test.cpp"
#define PROBLEM "https://judge.yosupo.jp/problem/maximum_independent_set"

#line 1 "utilities/fast_io.hpp"



#include <algorithm>
#include <array>
#include <cerrno>
#include <charconv>
#include <cstddef>
#include <cstdio>
#include <cstdlib>
#include <cstdint>
#include <cstring>
#include <iterator>
#include <string>
#include <sys/stat.h>
#include <type_traits>
#include <utility>
#include <unistd.h>
#include <vector>

namespace m1une {
namespace utilities {

struct FastOutput;

namespace internal {

// Shared with the convenience helpers in template.hpp.
inline FastOutput* standard_output_instance = nullptr;

// Detect std::begin(x), std::end(x).
template <class T, class = void>
struct is_range : std::false_type {};

template <class T>
struct is_range<T, std::void_t<
    decltype(std::begin(std::declval<T&>())),
    decltype(std::end(std::declval<T&>()))
>> : std::true_type {};

template <class T>
inline constexpr bool is_range_v = is_range<T>::value;

template <class T>
using range_reference_t = decltype(*std::begin(std::declval<T&>()));

template <class T>
using range_value_t = std::remove_cv_t<std::remove_reference_t<range_reference_t<T>>>;

template <class T, class = void>
struct range_stored_value {
    using type = range_value_t<T>;
};

template <class T>
struct range_stored_value<T, std::void_t<typename std::remove_cv_t<std::remove_reference_t<T>>::value_type>> {
    using type = typename std::remove_cv_t<std::remove_reference_t<T>>::value_type;
};

template <class T>
using range_stored_value_t = typename range_stored_value<T>::type;

// Treat strings and C strings as scalar output objects, not as ranges.
template <class T>
struct is_char_array : std::false_type {};

template <class T, std::size_t N>
struct is_char_array<T[N]>
    : std::bool_constant<std::is_same_v<std::remove_cv_t<T>, char>> {};

template <class T>
struct is_string_like
    : std::bool_constant<
          std::is_same_v<std::decay_t<T>, std::string>
          || std::is_same_v<std::decay_t<T>, const char*>
          || std::is_same_v<std::decay_t<T>, char*>
          || is_char_array<std::remove_reference_t<T>>::value
      > {};

template <class T>
inline constexpr bool is_string_like_v = is_string_like<T>::value;

// ModInt-like type: x.val() is printable, and x can be assigned from long long.
template <class T, class = void>
struct has_val_method : std::false_type {};

template <class T>
struct has_val_method<T, std::void_t<decltype(std::declval<const T&>().val())>>
    : std::true_type {};

template <class T>
inline constexpr bool has_val_method_v = has_val_method<T>::value;

template <class T, class = void>
struct has_static_mod_raw : std::false_type {};

template <class T>
struct has_static_mod_raw<
    T, std::void_t<decltype(T::mod()), decltype(T::raw(std::declval<uint32_t>()))>>
    : std::true_type {};

template <class T>
inline constexpr bool has_static_mod_raw_v = has_static_mod_raw<T>::value;

// libstdc++ before GCC 16 does not classify __int128 as an integral type in
// strict ISO modes such as -std=c++23. Keep the fast-I/O interface independent
// of that implementation detail.
template <class T>
inline constexpr bool is_integral_v =
    std::is_integral_v<T>
    || std::is_same_v<std::remove_cv_t<T>, __int128_t>
    || std::is_same_v<std::remove_cv_t<T>, __uint128_t>;

template <class T>
inline constexpr bool is_signed_v =
    std::is_signed_v<T>
    || std::is_same_v<std::remove_cv_t<T>, __int128_t>;

template <class T>
struct make_unsigned {
    using type = std::make_unsigned_t<T>;
};

template <>
struct make_unsigned<__int128_t> {
    using type = __uint128_t;
};

template <>
struct make_unsigned<__uint128_t> {
    using type = __uint128_t;
};

template <class T>
using make_unsigned_t = typename make_unsigned<std::remove_cv_t<T>>::type;

}  // namespace internal

struct FastInput {
    static constexpr int buffer_size = 1 << 20;

   private:
    std::FILE* _stream;
    char _buffer[buffer_size];
    int _position;
    int _length;
    int _file_descriptor;
    bool _streaming;

    bool refill() {
        _position = 0;
        if (_streaming) {
            ssize_t length;
            do {
                length = ::read(_file_descriptor, _buffer, buffer_size);
            } while (length < 0 && errno == EINTR);
            if (length <= 0) {
                _length = 0;
                return false;
            }
            _length = int(length);
        } else {
            _length = int(std::fread(_buffer, 1, buffer_size, _stream));
        }
        return _length != 0;
    }

    template <class T>
    bool read_integer_from_stream(T& value) {
        if (!skip_spaces()) return false;
        int c = read_char_raw();

        bool negative = false;
        if (c == '-') {
            negative = true;
            c = read_char_raw();
        }

        if constexpr (internal::is_signed_v<T>) {
            T result = 0;
            while ('0' <= c && c <= '9') {
                result = negative ? result * 10 - (c - '0')
                                  : result * 10 + (c - '0');
                c = read_char_raw();
            }
            value = result;
        } else {
            T result = 0;
            while ('0' <= c && c <= '9') {
                result = result * 10 + T(c - '0');
                c = read_char_raw();
            }
            value = negative ? T(0) - result : result;
        }
        return true;
    }

    bool prepare_number() {
        if (_length - _position >= 64) return true;
        const int remaining = _length - _position;
        if (remaining > 0) std::memmove(_buffer, _buffer + _position, remaining);
        const int added = int(std::fread(_buffer + remaining, 1, buffer_size - remaining, _stream));
        _position = 0;
        _length = remaining + added;
        if (_length < buffer_size) _buffer[_length] = '\0';
        return _length != 0;
    }

   public:
    explicit FastInput(std::FILE* stream = stdin)
        : _stream(stream),
          _position(0),
          _length(0),
          _file_descriptor(::fileno(stream)),
          _streaming([&] {
              struct stat status;
              return _file_descriptor >= 0
                     && ::fstat(_file_descriptor, &status) == 0
                     && !S_ISREG(status.st_mode);
          }()) {}

    FastInput(const FastInput&) = delete;
    FastInput& operator=(const FastInput&) = delete;

    int read_char_raw() {
        if (_position == _length && !refill()) return EOF;
        return _buffer[_position++];
    }

    bool skip_spaces() {
        int c = read_char_raw();
        while (c != EOF && c <= ' ') c = read_char_raw();
        if (c == EOF) return false;
        --_position;
        return true;
    }

    bool read(char& value) {
        if (!skip_spaces()) return false;
        value = char(read_char_raw());
        return true;
    }

    bool read(std::string& value) {
        if (!skip_spaces()) return false;
        value.clear();
        while (true) {
            const int begin = _position;
            while (_position < _length &&
                   static_cast<unsigned char>(_buffer[_position]) > ' ') {
                ++_position;
            }
            value.append(_buffer + begin, _position - begin);
            if (_position < _length) {
                ++_position;
                return true;
            }
            if (!refill()) return true;
        }
    }

    bool read(bool& value) {
        int x;
        if (!read(x)) return false;
        value = x != 0;
        return true;
    }

    template <class T>
    std::enable_if_t<
        internal::is_integral_v<T>
            && !std::is_same_v<std::remove_cv_t<T>, bool>
            && !std::is_same_v<std::remove_cv_t<T>, char>,
        bool
    >
    read(T& value) {
        if (_streaming) return read_integer_from_stream(value);
        if (!prepare_number()) return false;
        int c = static_cast<unsigned char>(_buffer[_position++]);
        while (c <= ' ') c = static_cast<unsigned char>(_buffer[_position++]);

        bool negative = false;
        if (c == '-') {
            negative = true;
            c = static_cast<unsigned char>(_buffer[_position++]);
        }

        if constexpr (internal::is_signed_v<T>) {
            T result = 0;
            while ('0' <= c && c <= '9') {
                const int first = c - '0';
                const int second = static_cast<unsigned char>(_buffer[_position]) - '0';
                if (0 <= second && second <= 9) {
                    result = negative ? result * 100 - (first * 10 + second)
                                      : result * 100 + (first * 10 + second);
                    ++_position;
                } else {
                    result = negative ? result * 10 - first : result * 10 + first;
                }
                c = static_cast<unsigned char>(_buffer[_position++]);
            }
            value = result;
        } else {
            T result = 0;
            while ('0' <= c && c <= '9') {
                const unsigned first = unsigned(c - '0');
                const int second = static_cast<unsigned char>(_buffer[_position]) - '0';
                if (0 <= second && second <= 9) {
                    result = result * 100 + T(first * 10 + unsigned(second));
                    ++_position;
                } else {
                    result = result * 10 + T(first);
                }
                c = static_cast<unsigned char>(_buffer[_position++]);
            }
            value = negative ? T(0) - result : result;
        }
        if (_position > _length) _position = _length;
        return true;
    }

    template <class T>
    std::enable_if_t<std::is_floating_point_v<T>, bool>
    read(T& value) {
        if (!skip_spaces()) return false;
        int c = read_char_raw();
        bool negative = false;
        if (c == '-' || c == '+') {
            negative = c == '-';
            c = read_char_raw();
        }

        long double result = 0;
        while ('0' <= c && c <= '9') {
            result = result * 10 + (c - '0');
            c = read_char_raw();
        }
        if (c == '.') {
            long double place = 0.1L;
            c = read_char_raw();
            while ('0' <= c && c <= '9') {
                result += (c - '0') * place;
                place *= 0.1L;
                c = read_char_raw();
            }
        }
        if (c == 'e' || c == 'E') {
            c = read_char_raw();
            bool exponent_negative = false;
            if (c == '-' || c == '+') {
                exponent_negative = c == '-';
                c = read_char_raw();
            }
            int exponent = 0;
            while ('0' <= c && c <= '9') {
                exponent = exponent * 10 + (c - '0');
                c = read_char_raw();
            }
            long double scale = 1;
            long double power = 10;
            while (exponent > 0) {
                if (exponent & 1) scale *= power;
                power *= power;
                exponent >>= 1;
            }
            result = exponent_negative ? result / scale : result * scale;
        }
        value = static_cast<T>(negative ? -result : result);
        return true;
    }

    template <class T>
    std::enable_if_t<
        internal::has_val_method_v<T>
            && !internal::is_integral_v<T>
            && !internal::is_range_v<T>,
        bool
    >
    read(T& value) {
        long long x;
        if (!read(x)) return false;
        if constexpr (internal::has_static_mod_raw_v<T>) {
            if (x >= 0 && uint64_t(x) < uint64_t(T::mod())) {
                value = T::raw(uint32_t(x));
            } else {
                value = T(x);
            }
        } else {
            value = T(x);
        }
        return true;
    }

    template <class First, class Second>
    bool read(std::pair<First, Second>& value) {
        if (!read(value.first)) return false;
        return read(value.second);
    }

    template <class Range>
    std::enable_if_t<
        internal::is_range_v<Range>
            && !internal::is_string_like_v<Range>,
        bool
    >
    read(Range& range) {
        using StoredValue = internal::range_stored_value_t<Range>;
        constexpr bool nested = internal::is_range_v<StoredValue>
                                && !internal::is_string_like_v<StoredValue>;

        for (auto&& value : range) {
            if constexpr (std::is_same_v<StoredValue, bool> && !nested) {
                bool x;
                if (!read(x)) return false;
                value = x;
            } else {
                if (!read(value)) return false;
            }
        }
        return true;
    }

    template <class First, class Second, class... Rest>
    bool read(First& first, Second& second, Rest&... rest) {
        if (!read(first)) return false;
        return read(second, rest...);
    }

    template <class T>
    FastInput& operator>>(T& value) {
        if (!read(value)) std::abort();
        return *this;
    }
};

struct FastOutput {
    static constexpr int buffer_size = 1 << 20;

   private:
    inline static const auto digit_quads = [] {
        std::array<char, 40000> result{};
        for (int i = 0; i < 10000; i++) {
            int value = i;
            for (int j = 3; j >= 0; j--) {
                result[4 * i + j] = char('0' + value % 10);
                value /= 10;
            }
        }
        return result;
    }();

    std::FILE* _stream;
    char _buffer[buffer_size];
    int _position;
    int _precision;
    std::chars_format _float_format;
    char _range_separator;
    std::string* _capture = nullptr;

    template <class T>
    std::string format_cell(const T& value) {
        std::string result;
        struct CaptureGuard {
            std::string*& target;
            std::string* previous;
            ~CaptureGuard() { target = previous; }
        } guard{_capture, _capture};
        _capture = &result;
        write(value);
        return result;
    }

    template <class Matrix>
    void write_aligned_matrix(const Matrix& matrix) {
        std::vector<std::vector<std::string>> rows;
        std::vector<std::size_t> widths;
        for (const auto& row : matrix) {
            auto& cells = rows.emplace_back();
            std::size_t column = 0;
            for (const auto& value : row) {
                cells.push_back(format_cell(value));
                if (column == widths.size()) widths.push_back(0);
                widths[column] = std::max(widths[column], cells.back().size());
                ++column;
            }
        }
        bool first = true;
        for (const auto& row : rows) {
            if (!first) write_char('\n');
            first = false;
            for (std::size_t column = 0; column < row.size(); ++column) {
                if (column != 0) write_char(_range_separator);
                for (std::size_t padding = row[column].size();
                     padding < widths[column]; ++padding) {
                    write_char(' ');
                }
                write(row[column]);
            }
        }
    }

   public:
    explicit FastOutput(std::FILE* stream = stdout)
        : _stream(stream),
          _position(0),
          _precision(6),
          _float_format(std::chars_format::general),
          _range_separator(' ') {
        if (_stream == stdout
            && internal::standard_output_instance == nullptr) {
            internal::standard_output_instance = this;
        }
    }

    FastOutput(const FastOutput&) = delete;
    FastOutput& operator=(const FastOutput&) = delete;

    ~FastOutput() {
        flush();
        if (internal::standard_output_instance == this) {
            internal::standard_output_instance = nullptr;
        }
    }

    void flush() {
        if (_position != 0) {
            std::fwrite(_buffer, 1, _position, _stream);
            _position = 0;
        }
        std::fflush(_stream);
    }

    void write_char(char c) {
        if (_capture != nullptr) {
            _capture->push_back(c);
            return;
        }
        if (_position == buffer_size) flush();
        _buffer[_position++] = c;
    }

    void write(const char* s) {
        while (*s != '\0') write_char(*s++);
    }

    void write(const std::string& s) {
        if (_capture != nullptr) {
            _capture->append(s);
            return;
        }
        std::size_t position = 0;
        while (position < s.size()) {
            if (_position == buffer_size) flush();
            const std::size_t copied =
                std::min<std::size_t>(buffer_size - _position, s.size() - position);
            std::memcpy(_buffer + _position, s.data() + position, copied);
            _position += int(copied);
            position += copied;
        }
    }

    void write(char c) {
        write_char(c);
    }

    void write(bool value) {
        write_char(value ? '1' : '0');
    }

    template <class T>
    std::enable_if_t<std::is_floating_point_v<T>>
    write(T value) {
        char digits[128];
        auto [end, error] = std::to_chars(
            digits,
            digits + sizeof(digits),
            value,
            _float_format,
            _precision
        );
        if (error != std::errc()) std::abort();
        for (const char* pointer = digits; pointer != end; pointer++) {
            write_char(*pointer);
        }
    }

    template <class T>
    std::enable_if_t<
        internal::is_integral_v<T>
            && !std::is_same_v<std::remove_cv_t<T>, bool>
            && !std::is_same_v<std::remove_cv_t<T>, char>
    >
    write(T value) {
        using Raw = std::remove_cv_t<T>;
        using Unsigned = internal::make_unsigned_t<Raw>;

        Unsigned magnitude;
        if constexpr (internal::is_signed_v<Raw>) {
            if (value < 0) {
                write_char('-');
                magnitude = Unsigned(0) - Unsigned(value);
            } else {
                magnitude = Unsigned(value);
            }
        } else {
            magnitude = value;
        }

        if (magnitude == 0) {
            write_char('0');
            return;
        }

        unsigned chunks[16];
        int count = 0;
        while (magnitude >= 10000) {
            const Unsigned quotient = magnitude / 10000;
            chunks[count++] = unsigned(magnitude - quotient * 10000);
            magnitude = quotient;
        }
        if (_capture == nullptr && _position > buffer_size - 64) flush();
        char captured[64];
        char* const begin = _capture != nullptr ? captured : _buffer + _position;
        char* destination = begin;
        const unsigned leading = unsigned(magnitude);
        const char* first = digit_quads.data() + 4 * leading;
        int skip = leading < 10 ? 3 : leading < 100 ? 2 : leading < 1000 ? 1 : 0;
        for (; skip < 4; skip++) *destination++ = first[skip];
        while (count--) {
            const char* digits = digit_quads.data() + 4 * chunks[count];
            std::memcpy(destination, digits, 4);
            destination += 4;
        }
        if (_capture != nullptr) {
            _capture->append(begin, destination - begin);
        } else {
            _position += int(destination - begin);
        }
    }

    template <class T>
    std::enable_if_t<
        internal::has_val_method_v<T>
            && !internal::is_integral_v<T>
            && !internal::is_range_v<T>
    >
    write(const T& value) {
        write(value.val());
    }

    template <class First, class Second>
    void write(const std::pair<First, Second>& value) {
        write(value.first);
        write_char(' ');
        write(value.second);
    }

    template <class Range>
    std::enable_if_t<
        internal::is_range_v<Range>
            && !internal::is_string_like_v<Range>
    >
    write(const Range& range) {
        using StoredValue = internal::range_stored_value_t<const Range>;
        constexpr bool nested = internal::is_range_v<StoredValue>
                                && !internal::is_string_like_v<StoredValue>;

        bool first = true;
        for (const auto& value : range) {
            if (!first) write_char(nested ? '\n' : _range_separator);
            first = false;
            if constexpr (std::is_same_v<StoredValue, bool> && !nested) {
                write(static_cast<bool>(value));
            } else {
                write(value);
            }
        }
    }

    template <class First, class... Rest>
    void print(const First& first, const Rest&... rest) {
        write(first);
        ((write_char(' '), write(rest)), ...);
    }

    void println() {
        write_char('\n');
    }

    void set_precision(int precision) {
        _precision = precision;
    }

    void set_fixed(int precision = 6) {
        _float_format = std::chars_format::fixed;
        _precision = precision;
    }

    void set_general(int precision = 6) {
        _float_format = std::chars_format::general;
        _precision = precision;
    }

    void set_range_separator(char separator) {
        _range_separator = separator;
    }

    template <class Matrix>
    void write_aligned(const Matrix& matrix) {
        using Row = internal::range_stored_value_t<const Matrix>;
        using Cell = internal::range_stored_value_t<const Row>;
        static_assert(internal::is_range_v<Row> && !internal::is_string_like_v<Row>,
                      "write_aligned requires a two-dimensional range");
        static_assert(!internal::is_range_v<Cell> || internal::is_string_like_v<Cell>,
                      "write_aligned requires scalar cells");
        write_aligned_matrix(matrix);
    }

    template <class Matrix>
    void println_aligned(const Matrix& matrix) {
        write_aligned(matrix);
        write_char('\n');
    }

    template <class... Args>
    void println(const Args&... args) {
        print(args...);
        write_char('\n');
    }

    template <class T>
    FastOutput& operator<<(const T& value) {
        write(value);
        return *this;
    }
};

}  // namespace utilities
}  // namespace m1une


#line 4 "verify/graph/library_checker_maximum_independent_set.test.cpp"

#include <bits/stdc++.h>
using namespace std;

#line 1 "graph/graph.hpp"



#line 8 "graph/graph.hpp"

namespace m1une {
namespace graph {

template <class T = int>
struct Edge {
    using cost_type = T;

    int from;
    int to;
    T cost;
    int id;
    bool alive;

    Edge() : from(-1), to(-1), cost(T()), id(-1), alive(true) {}
    Edge(int from_, int to_, T cost_ = T(1), int id_ = -1, bool alive_ = true)
        : from(from_), to(to_), cost(cost_), id(id_), alive(alive_) {}

    int other(int v) const {
        assert(v == from || v == to);
        return from ^ to ^ v;
    }
};

template <class T = int>
struct Graph {
    using edge_type = Edge<T>;
    using cost_type = T;

   private:
    struct EdgePositions {
        std::array<std::pair<int, int>, 2> value{};
        int size = 0;

        void push_back(std::pair<int, int> position) {
            assert(size < 2);
            value[size++] = position;
        }
    };

    int _n;
    int _edge_count;
    std::vector<std::vector<edge_type>> _g;
    std::vector<EdgePositions> _edge_positions;

   public:
    Graph() : _n(0), _edge_count(0) {}
    explicit Graph(int n) : _n(n), _edge_count(0), _g(n) {
        assert(0 <= n);
    }

    int size() const {
        return _n;
    }

    bool empty() const {
        return _n == 0;
    }

    int edge_count() const {
        return _edge_count;
    }

    int add_vertex() {
        _g.emplace_back();
        return _n++;
    }

    int add_directed_edge(int from, int to, T cost = T(1)) {
        assert(0 <= from && from < _n);
        assert(0 <= to && to < _n);
        int id = _edge_count++;
        int idx = int(_g[from].size());
        _g[from].push_back(edge_type(from, to, cost, id));
        _edge_positions.emplace_back();
        _edge_positions.back().push_back({from, idx});
        return id;
    }

    int add_edge(int u, int v, T cost = T(1)) {
        assert(0 <= u && u < _n);
        assert(0 <= v && v < _n);
        int id = _edge_count++;
        int u_idx = int(_g[u].size());
        _g[u].push_back(edge_type(u, v, cost, id));
        int v_idx = int(_g[v].size());
        _g[v].push_back(edge_type(v, u, cost, id));
        _edge_positions.emplace_back();
        _edge_positions.back().push_back({u, u_idx});
        _edge_positions.back().push_back({v, v_idx});
        return id;
    }

    void set_edge_alive(int id, bool alive) {
        assert(0 <= id && id < _edge_count);
        for (int i = 0; i < _edge_positions[id].size; ++i) {
            auto [v, idx] = _edge_positions[id].value[i];
            _g[v][idx].alive = alive;
        }
    }

    void erase_edge(int id) {
        set_edge_alive(id, false);
    }

    void revive_edge(int id) {
        set_edge_alive(id, true);
    }

    bool is_edge_alive(int id) const {
        assert(0 <= id && id < _edge_count);
        assert(_edge_positions[id].size != 0);
        auto [v, idx] = _edge_positions[id].value[0];
        return _g[v][idx].alive;
    }

    const std::vector<edge_type>& operator[](int v) const {
        assert(0 <= v && v < _n);
        return _g[v];
    }

    std::vector<edge_type>& operator[](int v) {
        assert(0 <= v && v < _n);
        return _g[v];
    }

    const std::vector<std::vector<edge_type>>& adjacency() const {
        return _g;
    }

    std::vector<std::vector<edge_type>>& adjacency() {
        return _g;
    }

    std::vector<edge_type> edges(bool include_inactive = false) const {
        std::vector<edge_type> result;
        result.reserve(_edge_count);
        std::vector<char> used(_edge_count, false);
        for (int v = 0; v < _n; v++) {
            for (const auto& e : _g[v]) {
                if (!include_inactive && !e.alive) continue;
                if (0 <= e.id && e.id < _edge_count) {
                    if (used[e.id]) continue;
                    used[e.id] = true;
                }
                result.push_back(e);
            }
        }
        return result;
    }

    Graph reversed() const {
        Graph result(_n);
        result._edge_count = _edge_count;
        result._edge_positions.assign(_edge_count, {});
        for (int v = 0; v < _n; v++) {
            for (const auto& e : _g[v]) {
                int idx = int(result._g[e.to].size());
                result._g[e.to].push_back(edge_type(e.to, e.from, e.cost, e.id, e.alive));
                if (0 <= e.id && e.id < _edge_count) result._edge_positions[e.id].push_back({e.to, idx});
            }
        }
        return result;
    }
};

}  // namespace graph
}  // namespace m1une


#line 1 "graph/maximum_clique.hpp"



#line 7 "graph/maximum_clique.hpp"

#line 9 "graph/maximum_clique.hpp"

namespace m1une {
namespace graph {

struct MaximumCliqueResult {
    std::vector<int> vertices;

    int size() const {
        return int(vertices.size());
    }

    bool empty() const {
        return vertices.empty();
    }
};

struct MaximumIndependentSetResult {
    std::vector<int> vertices;

    int size() const {
        return int(vertices.size());
    }

    bool empty() const {
        return vertices.empty();
    }
};

struct MinimumVertexCoverResult {
    std::vector<int> vertices;

    int size() const {
        return int(vertices.size());
    }

    bool empty() const {
        return vertices.empty();
    }
};

namespace detail {

struct MaximumIndependentSetBranching {
    int n;
    std::vector<std::vector<char>> adjacent;
    std::vector<std::vector<int>> graph;

    explicit MaximumIndependentSetBranching(const std::vector<std::vector<char>>& adjacent_)
        : n(int(adjacent_.size())), adjacent(adjacent_), graph(n) {
        for (int v = 0; v < n; v++) {
            for (int to = 0; to < n; to++) {
                if (adjacent[v][to]) graph[v].push_back(to);
            }
        }
    }

    std::vector<int> solve_path(const std::vector<int>& order) const {
        int m = int(order.size());
        if (m == 0) return {};

        std::vector<int> dp0(m, 0), dp1(m, 0);
        dp1[0] = 1;
        for (int i = 1; i < m; i++) {
            dp0[i] = std::max(dp0[i - 1], dp1[i - 1]);
            dp1[i] = dp0[i - 1] + 1;
        }

        std::vector<int> result;
        int state = (dp1[m - 1] > dp0[m - 1] ? 1 : 0);
        for (int i = m - 1; i >= 0; i--) {
            if (state == 1) {
                result.push_back(order[i]);
                state = 0;
            } else if (i > 0) {
                state = (dp1[i - 1] > dp0[i - 1] ? 1 : 0);
            }
        }
        return result;
    }

    std::vector<int> solve_cycle(const std::vector<int>& order) const {
        int m = int(order.size());
        if (m == 0) return {};
        if (m == 1) return {order[0]};

        std::vector<int> without_first(order.begin() + 1, order.end());
        auto result_without = solve_path(without_first);

        std::vector<int> result_with = {order[0]};
        if (m >= 4) {
            std::vector<int> middle(order.begin() + 2, order.end() - 1);
            auto middle_result = solve_path(middle);
            result_with.insert(result_with.end(), middle_result.begin(), middle_result.end());
        }

        return (result_with.size() > result_without.size() ? result_with : result_without);
    }

    std::vector<int> solve_degree_at_most_two(const std::vector<char>& active,
                                              const std::vector<int>& degree) const {
        std::vector<int> result;
        std::vector<char> visited(n, false);

        for (int s = 0; s < n; s++) {
            if (!active[s] || visited[s]) continue;

            std::vector<int> component;
            std::vector<int> stack = {s};
            visited[s] = true;
            for (int it = 0; it < int(stack.size()); it++) {
                int v = stack[it];
                component.push_back(v);
                for (int to : graph[v]) {
                    if (!active[to] || visited[to]) continue;
                    visited[to] = true;
                    stack.push_back(to);
                }
            }

            if (component.size() == 1) {
                result.push_back(component[0]);
                continue;
            }

            int endpoint = -1;
            for (int v : component) {
                if (degree[v] <= 1) {
                    endpoint = v;
                    break;
                }
            }

            std::vector<int> order;
            if (endpoint != -1) {
                int prev = -1, cur = endpoint;
                while (cur != -1) {
                    order.push_back(cur);
                    int next = -1;
                    for (int to : graph[cur]) {
                        if (active[to] && to != prev) {
                            next = to;
                            break;
                        }
                    }
                    prev = cur;
                    cur = next;
                }
                auto part = solve_path(order);
                result.insert(result.end(), part.begin(), part.end());
            } else {
                int start = component[0];
                int first = -1;
                for (int to : graph[start]) {
                    if (active[to]) {
                        first = to;
                        break;
                    }
                }
                assert(first != -1);

                order.push_back(start);
                int prev = start, cur = first;
                while (cur != start) {
                    order.push_back(cur);
                    int next = -1;
                    for (int to : graph[cur]) {
                        if (active[to] && to != prev) {
                            next = to;
                            break;
                        }
                    }
                    assert(next != -1);
                    prev = cur;
                    cur = next;
                }
                auto part = solve_cycle(order);
                result.insert(result.end(), part.begin(), part.end());
            }
        }

        return result;
    }

    std::vector<int> solve(std::vector<char> active) const {
        int active_count = 0;
        int max_degree = -1;
        int branch_vertex = -1;
        std::vector<int> degree(n, 0);

        for (int v = 0; v < n; v++) {
            if (!active[v]) continue;
            active_count++;
            for (int to : graph[v]) {
                if (active[to]) degree[v]++;
            }
            if (degree[v] > max_degree) {
                max_degree = degree[v];
                branch_vertex = v;
            }
        }

        if (active_count == 0) return {};
        if (max_degree <= 2) {
            auto result = solve_degree_at_most_two(active, degree);
            std::sort(result.begin(), result.end());
            return result;
        }

        auto without = active;
        without[branch_vertex] = false;
        auto result_without = solve(without);

        auto with = active;
        with[branch_vertex] = false;
        for (int to : graph[branch_vertex]) with[to] = false;
        auto result_with = solve(with);
        result_with.push_back(branch_vertex);

        auto result = (result_with.size() > result_without.size() ? result_with : result_without);
        std::sort(result.begin(), result.end());
        return result;
    }

    std::vector<int> solve() const {
        std::vector<char> active(n, true);
        return solve(active);
    }
};

template <class T>
std::vector<std::vector<char>> undirected_adjacency_matrix(const Graph<T>& g) {
    int n = g.size();
    std::vector<std::vector<char>> adjacent(n, std::vector<char>(n, false));
    for (const auto& e : g.edges()) {
        if (e.from == e.to) continue;
        adjacent[e.from][e.to] = true;
        adjacent[e.to][e.from] = true;
    }
    return adjacent;
}

std::vector<std::vector<char>> complement_adjacency_matrix(const std::vector<std::vector<char>>& adjacent) {
    int n = int(adjacent.size());
    std::vector<std::vector<char>> complement(n, std::vector<char>(n, false));
    for (int i = 0; i < n; i++) {
        for (int j = i + 1; j < n; j++) {
            if (adjacent[i][j]) continue;
            complement[i][j] = true;
            complement[j][i] = true;
        }
    }
    return complement;
}

}  // namespace detail

template <class T>
bool is_clique(const Graph<T>& g, const std::vector<int>& vertices) {
    auto adjacent = detail::undirected_adjacency_matrix(g);
    for (int v : vertices) {
        assert(0 <= v && v < g.size());
    }
    for (int i = 0; i < int(vertices.size()); i++) {
        for (int j = i + 1; j < int(vertices.size()); j++) {
            if (!adjacent[vertices[i]][vertices[j]]) return false;
        }
    }
    return true;
}

template <class T>
bool is_independent_set(const Graph<T>& g, const std::vector<int>& vertices) {
    auto adjacent = detail::undirected_adjacency_matrix(g);
    for (int v : vertices) {
        assert(0 <= v && v < g.size());
    }
    for (int i = 0; i < int(vertices.size()); i++) {
        for (int j = i + 1; j < int(vertices.size()); j++) {
            if (adjacent[vertices[i]][vertices[j]]) return false;
        }
    }
    return true;
}

template <class T>
bool is_vertex_cover(const Graph<T>& g, const std::vector<int>& vertices) {
    std::vector<char> selected(g.size(), false);
    for (int v : vertices) {
        assert(0 <= v && v < g.size());
        selected[v] = true;
    }
    for (const auto& e : g.edges()) {
        if (e.from == e.to) continue;
        if (!selected[e.from] && !selected[e.to]) return false;
    }
    return true;
}

template <class T>
MaximumCliqueResult maximum_clique(const Graph<T>& g) {
    auto adjacent = detail::undirected_adjacency_matrix(g);
    auto complement = detail::complement_adjacency_matrix(adjacent);
    detail::MaximumIndependentSetBranching solver(complement);
    return MaximumCliqueResult{solver.solve()};
}

template <class T>
int maximum_clique_size(const Graph<T>& g) {
    return maximum_clique(g).size();
}

template <class T>
MaximumIndependentSetResult maximum_independent_set(const Graph<T>& g) {
    auto adjacent = detail::undirected_adjacency_matrix(g);
    detail::MaximumIndependentSetBranching solver(adjacent);
    return MaximumIndependentSetResult{solver.solve()};
}

template <class T>
int maximum_independent_set_size(const Graph<T>& g) {
    return maximum_independent_set(g).size();
}

template <class T>
MinimumVertexCoverResult minimum_vertex_cover(const Graph<T>& g) {
    auto independent = maximum_independent_set(g);
    std::vector<char> in_independent(g.size(), false);
    for (int v : independent.vertices) in_independent[v] = true;

    MinimumVertexCoverResult result;
    for (int v = 0; v < g.size(); v++) {
        if (!in_independent[v]) result.vertices.push_back(v);
    }
    return result;
}

template <class T>
int minimum_vertex_cover_size(const Graph<T>& g) {
    return minimum_vertex_cover(g).size();
}

}  // namespace graph
}  // namespace m1une


#line 10 "verify/graph/library_checker_maximum_independent_set.test.cpp"

int main() {
    m1une::utilities::FastInput fast_input;
    m1une::utilities::FastOutput fast_output;

    int N, M;
    fast_input >> N >> M;
    m1une::graph::Graph<> g(N);
    while (M--) {
        int u, v;
        fast_input >> u >> v;
        g.add_edge(u, v);
    }
    auto independent = m1une::graph::maximum_independent_set(g);
    fast_output << independent.size() << '\n';
    for (int x : independent.vertices) {
        fast_output << x << ' ';
    }
    fast_output << '\n';
}
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