verify/graph/three_edge_connected_components.test.cpp

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Last update: 2026-10-06 01:57:24+09:00
Problem: https://judge.yosupo.jp/problem/three_edge_connected_components

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Code

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

#include "../../graph/three_edge_connected_components.hpp"

#include <algorithm>
#include <cassert>
#include <cstdint>
#include "../../utilities/fast_io.hpp"
#include <queue>
#include <vector>

namespace {

using Graph = m1une::graph::Graph<>;
using Result = m1une::graph::ThreeEdgeConnectedComponentsResult;

int naive_edge_connectivity(const Graph& graph, int source, int sink) {
    const int n = graph.size();
    std::vector<std::vector<int>> capacity(n, std::vector<int>(n, 0));
    for (const auto& edge : graph.edges()) {
        if (edge.from == edge.to) continue;
        capacity[edge.from][edge.to]++;
        capacity[edge.to][edge.from]++;
    }

    int flow = 0;
    while (flow < 3) {
        std::vector<int> parent(n, -1);
        std::queue<int> queue;
        parent[source] = source;
        queue.push(source);
        while (!queue.empty() && parent[sink] == -1) {
            int vertex = queue.front();
            queue.pop();
            for (int to = 0; to < n; to++) {
                if (capacity[vertex][to] == 0 || parent[to] != -1) continue;
                parent[to] = vertex;
                queue.push(to);
            }
        }
        if (parent[sink] == -1) break;
        for (int vertex = sink; vertex != source; vertex = parent[vertex]) {
            capacity[parent[vertex]][vertex]--;
            capacity[vertex][parent[vertex]]++;
        }
        flow++;
    }
    return flow;
}

void validate(const Graph& graph) {
    Result result = m1une::graph::three_edge_connected_components(graph);
    assert(result.component_of_vertex.size() == std::size_t(graph.size()));

    std::vector<int> occurrence(graph.size(), 0);
    for (int component = 0; component < result.component_count(); component++) {
        assert(!result.components[component].empty());
        for (int vertex : result.components[component]) {
            assert(0 <= vertex && vertex < graph.size());
            assert(result.component_of_vertex[vertex] == component);
            occurrence[vertex]++;
        }
    }
    for (int count : occurrence) assert(count == 1);

    for (int first = 0; first < graph.size(); first++) {
        for (int second = 0; second < graph.size(); second++) {
            bool expected = first == second || naive_edge_connectivity(graph, first, second) >= 3;
            assert(result.same(first, second) == expected);
        }
    }
}

void test_fixed() {
    validate(Graph());
    validate(Graph(1));

    Graph parallel(2);
    parallel.add_edge(0, 1);
    parallel.add_edge(0, 1);
    int third = parallel.add_edge(0, 1);
    validate(parallel);
    assert(m1une::graph::three_edge_connected_components(parallel).same(0, 1));
    parallel.erase_edge(third);
    validate(parallel);
    assert(!m1une::graph::three_edge_connected_components(parallel).same(0, 1));
    parallel.revive_edge(third);
    validate(parallel);

    Graph complete(4);
    for (int from = 0; from < 4; from++) {
        for (int to = from + 1; to < 4; to++) complete.add_edge(from, to);
    }
    complete.add_edge(0, 0);
    validate(complete);
    assert(m1une::graph::three_edge_connected_components(complete).component_count() == 1);

    Graph joined(8);
    for (int offset : {0, 4}) {
        for (int from = offset; from < offset + 4; from++) {
            for (int to = from + 1; to < offset + 4; to++) joined.add_edge(from, to);
        }
    }
    joined.add_edge(0, 4);
    joined.add_edge(1, 5);
    validate(joined);
    auto joined_result = m1une::graph::three_edge_connected_components(joined);
    assert(joined_result.component_count() == 2);
    assert(joined_result.same(0, 3));
    assert(joined_result.same(4, 7));
    assert(!joined_result.same(0, 4));
}

void test_randomized() {
    std::uint64_t state = 123456789;
    auto random = [&]() {
        state ^= state << 7;
        state ^= state >> 9;
        return state;
    };

    for (int trial = 0; trial < 500; trial++) {
        int n = int(random() % 9);
        Graph graph(n);
        int edge_count = int(random() % 26);
        for (int i = 0; i < edge_count && n > 0; i++) {
            int id = graph.add_edge(int(random() % n), int(random() % n));
            if (random() % 7 == 0) graph.erase_edge(id);
        }
        validate(graph);
    }
}

void test_deep_graph() {
    const int n = 50000;
    Graph graph(n);
    for (int vertex = 1; vertex < n; vertex++) graph.add_edge(vertex - 1, vertex);
    Result result = m1une::graph::three_edge_connected_components(graph);
    assert(result.component_count() == n);
}

}  // namespace

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

    test_fixed();
    test_randomized();
    test_deep_graph();
    int n, edge_count;
    fast_input >> n >> edge_count;
    Graph graph(n);
    while (edge_count--) {
        int from, to;
        fast_input >> from >> to;
        graph.add_edge(from, to);
    }

    Result result = m1une::graph::three_edge_connected_components(graph);
    fast_output << result.component_count() << '\n';
    for (const auto& component : result.components) {
        fast_output << component.size();
        for (int vertex : component) fast_output << ' ' << vertex;
        fast_output << '\n';
    }
}

#line 1 "verify/graph/three_edge_connected_components.test.cpp"
#define PROBLEM "https://judge.yosupo.jp/problem/three_edge_connected_components"

#line 1 "graph/three_edge_connected_components.hpp"



#include <algorithm>
#include <cassert>
#include <numeric>
#include <utility>
#include <vector>

#line 1 "graph/graph.hpp"



#include <array>
#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 11 "graph/three_edge_connected_components.hpp"

namespace m1une {
namespace graph {

struct ThreeEdgeConnectedComponentsResult {
    std::vector<std::vector<int>> components;
    std::vector<int> component_of_vertex;

    int component_count() const {
        return int(components.size());
    }

    bool same(int first, int second) const {
        assert(0 <= first && first < int(component_of_vertex.size()));
        assert(0 <= second && second < int(component_of_vertex.size()));
        return component_of_vertex[first] == component_of_vertex[second];
    }
};

namespace internal {

// Maintains every component as a circular linked list. Swapping two successors
// concatenates two different lists in O(1) time.
struct ThreeEdgeComponentCycles {
    std::vector<int> next;

    explicit ThreeEdgeComponentCycles(int n) : next(n) {
        std::iota(next.begin(), next.end(), 0);
    }

    void unite(int first, int second) {
        std::swap(next[first], next[second]);
    }

    ThreeEdgeConnectedComponentsResult build_result() const {
        const int n = int(next.size());
        ThreeEdgeConnectedComponentsResult result;
        result.component_of_vertex.assign(n, -1);
        for (int first = 0; first < n; first++) {
            if (result.component_of_vertex[first] != -1) continue;
            const int component = result.component_count();
            result.components.emplace_back();
            int vertex = first;
            do {
                result.component_of_vertex[vertex] = component;
                result.components.back().push_back(vertex);
                vertex = next[vertex];
            } while (vertex != first);
        }
        return result;
    }
};

}  // namespace internal

// Decomposes an undirected multigraph into maximal vertex sets joined by at
// least three edge-disjoint paths. This is an iterative form of Tsin's
// one-pass contraction algorithm.
template <class T>
ThreeEdgeConnectedComponentsResult three_edge_connected_components(
    const Graph<T>& graph
) {
    const int n = graph.size();
    const int edge_count = graph.edge_count();

#ifndef NDEBUG
    std::vector<int> incidence_count(edge_count, 0);
    for (int vertex = 0; vertex < n; vertex++) {
        for (const Edge<T>& edge : graph[vertex]) {
            if (!edge.alive) continue;
            assert(edge.from == vertex);
            assert(0 <= edge.to && edge.to < n);
            assert(0 <= edge.id && edge.id < edge_count);
            incidence_count[edge.id]++;
        }
    }
    for (int edge_id = 0; edge_id < edge_count; edge_id++) {
        if (incidence_count[edge_id] != 0) assert(incidence_count[edge_id] == 2);
    }
#endif

    const int none = n;
    std::vector<int> enter(n, -1);
    std::vector<int> leave(n, 0);
    std::vector<int> low(n, none);
    std::vector<int> degree(n, 0);
    std::vector<int> path(n, none);
    std::vector<int> parent(n, -1);
    std::vector<int> parent_edge(n, -1);
    std::vector<int> next_edge(n, 0);
    std::vector<int> dfs_stack;
    internal::ThreeEdgeComponentCycles component_cycles(n);
    int timer = 0;

    auto absorb = [&](int vertex, int other) {
        component_cycles.unite(vertex, other);
        degree[vertex] += degree[other];
    };

    auto process_visited_edge = [&](int vertex, int to) {
        if (enter[to] < enter[vertex]) {
            degree[vertex]++;
            low[vertex] = std::min(low[vertex], enter[to]);
            return;
        }

        degree[vertex]--;
        int current = path[vertex];
        while (current != none && enter[current] <= enter[to] && enter[to] < leave[current]) {
            absorb(vertex, current);
            current = path[current];
        }
        path[vertex] = current;
    };

    auto process_child = [&](int vertex, int child) {
        if (path[child] == none && degree[child] <= 1) {
            degree[vertex] += degree[child];
            low[vertex] = std::min(low[vertex], low[child]);
            return;
        }

        int current = child;
        if (degree[child] == 0) current = path[child];
        assert(current != none);
        if (low[current] < low[vertex]) {
            low[vertex] = low[current];
            std::swap(current, path[vertex]);
        }
        while (current != none) {
            absorb(vertex, current);
            current = path[current];
        }
    };

    for (int root = 0; root < n; root++) {
        if (enter[root] != -1) continue;
        enter[root] = timer++;
        dfs_stack.push_back(root);

        while (!dfs_stack.empty()) {
            const int vertex = dfs_stack.back();
            if (next_edge[vertex] < int(graph[vertex].size())) {
                const Edge<T>& edge = graph[vertex][next_edge[vertex]++];
                if (!edge.alive || edge.from == edge.to || edge.id == parent_edge[vertex]) continue;
                const int to = edge.to;
                if (enter[to] == -1) {
                    parent[to] = vertex;
                    parent_edge[to] = edge.id;
                    enter[to] = timer++;
                    dfs_stack.push_back(to);
                } else {
                    process_visited_edge(vertex, to);
                }
                continue;
            }

            leave[vertex] = timer;
            dfs_stack.pop_back();
            if (parent[vertex] != -1) process_child(parent[vertex], vertex);
        }
    }

    return component_cycles.build_result();
}

}  // namespace graph
}  // namespace m1une


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

#line 7 "verify/graph/three_edge_connected_components.test.cpp"
#include <cstdint>
#line 1 "utilities/fast_io.hpp"



#line 6 "utilities/fast_io.hpp"
#include <cerrno>
#include <charconv>
#include <cstddef>
#include <cstdio>
#include <cstdlib>
#line 12 "utilities/fast_io.hpp"
#include <cstring>
#include <iterator>
#include <string>
#include <sys/stat.h>
#include <type_traits>
#line 18 "utilities/fast_io.hpp"
#include <unistd.h>
#line 20 "utilities/fast_io.hpp"

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 9 "verify/graph/three_edge_connected_components.test.cpp"
#include <queue>
#line 11 "verify/graph/three_edge_connected_components.test.cpp"

namespace {

using Graph = m1une::graph::Graph<>;
using Result = m1une::graph::ThreeEdgeConnectedComponentsResult;

int naive_edge_connectivity(const Graph& graph, int source, int sink) {
    const int n = graph.size();
    std::vector<std::vector<int>> capacity(n, std::vector<int>(n, 0));
    for (const auto& edge : graph.edges()) {
        if (edge.from == edge.to) continue;
        capacity[edge.from][edge.to]++;
        capacity[edge.to][edge.from]++;
    }

    int flow = 0;
    while (flow < 3) {
        std::vector<int> parent(n, -1);
        std::queue<int> queue;
        parent[source] = source;
        queue.push(source);
        while (!queue.empty() && parent[sink] == -1) {
            int vertex = queue.front();
            queue.pop();
            for (int to = 0; to < n; to++) {
                if (capacity[vertex][to] == 0 || parent[to] != -1) continue;
                parent[to] = vertex;
                queue.push(to);
            }
        }
        if (parent[sink] == -1) break;
        for (int vertex = sink; vertex != source; vertex = parent[vertex]) {
            capacity[parent[vertex]][vertex]--;
            capacity[vertex][parent[vertex]]++;
        }
        flow++;
    }
    return flow;
}

void validate(const Graph& graph) {
    Result result = m1une::graph::three_edge_connected_components(graph);
    assert(result.component_of_vertex.size() == std::size_t(graph.size()));

    std::vector<int> occurrence(graph.size(), 0);
    for (int component = 0; component < result.component_count(); component++) {
        assert(!result.components[component].empty());
        for (int vertex : result.components[component]) {
            assert(0 <= vertex && vertex < graph.size());
            assert(result.component_of_vertex[vertex] == component);
            occurrence[vertex]++;
        }
    }
    for (int count : occurrence) assert(count == 1);

    for (int first = 0; first < graph.size(); first++) {
        for (int second = 0; second < graph.size(); second++) {
            bool expected = first == second || naive_edge_connectivity(graph, first, second) >= 3;
            assert(result.same(first, second) == expected);
        }
    }
}

void test_fixed() {
    validate(Graph());
    validate(Graph(1));

    Graph parallel(2);
    parallel.add_edge(0, 1);
    parallel.add_edge(0, 1);
    int third = parallel.add_edge(0, 1);
    validate(parallel);
    assert(m1une::graph::three_edge_connected_components(parallel).same(0, 1));
    parallel.erase_edge(third);
    validate(parallel);
    assert(!m1une::graph::three_edge_connected_components(parallel).same(0, 1));
    parallel.revive_edge(third);
    validate(parallel);

    Graph complete(4);
    for (int from = 0; from < 4; from++) {
        for (int to = from + 1; to < 4; to++) complete.add_edge(from, to);
    }
    complete.add_edge(0, 0);
    validate(complete);
    assert(m1une::graph::three_edge_connected_components(complete).component_count() == 1);

    Graph joined(8);
    for (int offset : {0, 4}) {
        for (int from = offset; from < offset + 4; from++) {
            for (int to = from + 1; to < offset + 4; to++) joined.add_edge(from, to);
        }
    }
    joined.add_edge(0, 4);
    joined.add_edge(1, 5);
    validate(joined);
    auto joined_result = m1une::graph::three_edge_connected_components(joined);
    assert(joined_result.component_count() == 2);
    assert(joined_result.same(0, 3));
    assert(joined_result.same(4, 7));
    assert(!joined_result.same(0, 4));
}

void test_randomized() {
    std::uint64_t state = 123456789;
    auto random = [&]() {
        state ^= state << 7;
        state ^= state >> 9;
        return state;
    };

    for (int trial = 0; trial < 500; trial++) {
        int n = int(random() % 9);
        Graph graph(n);
        int edge_count = int(random() % 26);
        for (int i = 0; i < edge_count && n > 0; i++) {
            int id = graph.add_edge(int(random() % n), int(random() % n));
            if (random() % 7 == 0) graph.erase_edge(id);
        }
        validate(graph);
    }
}

void test_deep_graph() {
    const int n = 50000;
    Graph graph(n);
    for (int vertex = 1; vertex < n; vertex++) graph.add_edge(vertex - 1, vertex);
    Result result = m1une::graph::three_edge_connected_components(graph);
    assert(result.component_count() == n);
}

}  // namespace

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

    test_fixed();
    test_randomized();
    test_deep_graph();
    int n, edge_count;
    fast_input >> n >> edge_count;
    Graph graph(n);
    while (edge_count--) {
        int from, to;
        fast_input >> from >> to;
        graph.add_edge(from, to);
    }

    Result result = m1une::graph::three_edge_connected_components(graph);
    fast_output << result.component_count() << '\n';
    for (const auto& component : result.components) {
        fast_output << component.size();
        for (int vertex : component) fast_output << ' ' << vertex;
        fast_output << '\n';
    }
}

m1une's library

This documentation is automatically generated by online-judge-tools/verification-helper

verify/graph/three_edge_connected_components.test.cpp

Depends on

Code