Cycle Detection (Directed) (verify/graph/cycle_directed.test.cpp)

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• Last update: 2025-05-22 14:15:11+02:00
• Problem: https://judge.yosupo.jp/problem/cycle_detection

Depends on

• cp-algo/graph/base.hpp
• cp-algo/graph/cycle.hpp
• cp-algo/graph/edge_types.hpp
• cp-algo/structures/stack_union.hpp

Code

// @brief Cycle Detection (Directed)
#define PROBLEM "https://judge.yosupo.jp/problem/cycle_detection"
#pragma GCC optimize("Ofast,unroll-loops")
#include <bits/stdc++.h>
#include "blazingio/blazingio.min.hpp"
#include "cp-algo/graph/cycle.hpp"

using namespace std;
using namespace cp_algo::graph;

void solve() {
    int n, m;
    cin >> n >> m;
    graph<directed> g(n);
    g.read_edges(m);
    auto res = find_cycle(g);
    if(empty(res)) {
        cout << -1 << "\n";
    } else {
        cout << size(res) << "\n";
        for(auto it: res) {cout << it / 2 << '\n';}
    }
}

signed main() {
    //freopen("input.txt", "r", stdin);
    ios::sync_with_stdio(0);
    cin.tie(0);
    int t = 1;
    while(t--) {
        solve();
    }
}

#line 1 "verify/graph/cycle_directed.test.cpp"
// @brief Cycle Detection (Directed)
#define PROBLEM "https://judge.yosupo.jp/problem/cycle_detection"
#pragma GCC optimize("Ofast,unroll-loops")
#include <bits/stdc++.h>
#line 1 "blazingio/blazingio.min.hpp"
// NOLINTBEGIN
// clang-format off
// DO NOT REMOVE THIS MESSAGE. The mess that follows is a minified build of
// https://github.com/purplesyringa/blazingio. Refer to the repository for
// a human-readable version and documentation.
// Options: cbfoiedrhWLMXaIaAn
#define M$(x,...)_mm256_##x##_epi8(__VA_ARGS__)
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#define cin i$
#define cout o$
#ifdef ONLINE_JUDGE
#define cerr e$
#define clog e$
#endif
// End of blazingio
// NOLINTEND
// clang-format on
#line 1 "cp-algo/graph/cycle.hpp"


#line 1 "cp-algo/graph/base.hpp"


#line 1 "cp-algo/graph/edge_types.hpp"


#line 5 "cp-algo/graph/edge_types.hpp"
namespace cp_algo::graph {
    using node_index = int;
    struct edge_base {
        node_index to;

        edge_base() {}
        edge_base(node_index v): to(v) {}

        static auto read(node_index v0 = 0) {
            node_index u, v;
            std::cin >> u >> v;
            return std::pair{u - v0, edge_base(v - v0)};
        }

        edge_base backedge(int from) const {
            return {from};
        }
    };

    struct weighted_edge: edge_base {
        int64_t w;

        weighted_edge() {}
        weighted_edge(node_index v, int64_t w): edge_base(v), w(w) {}

        static auto read(node_index v0 = 0) {
            node_index u, v;
            int64_t w;
            std::cin >> u >> v >> w;
            return std::pair{u - v0, weighted_edge{v - v0, w}};
        }

        weighted_edge backedge(node_index from) const {
            return {from, w};
        }
    };

    template<typename edge>
    concept edge_type = std::is_base_of_v<edge_base, edge>;
    template<typename edge>
    concept weighted_edge_type = std::is_base_of_v<weighted_edge, edge>;
}

#line 1 "cp-algo/structures/stack_union.hpp"


#line 5 "cp-algo/structures/stack_union.hpp"
namespace cp_algo::structures {
    template<class datatype>
    struct stack_union {
        stack_union(int n = 0): head(n), next(1), data(1) {}

        void push(int v, datatype const& vdata) {
            next.push_back(head[v]);
            head[v] = (int)std::size(next) - 1;
            data.push_back(vdata);
        }
        template<typename... Args>
        void emplace(int v, Args&&... vdata) {
            next.push_back(head[v]);
            head[v] = size(next) - 1;
            data.emplace_back(std::forward<Args...>(vdata...));
        }

        void reserve(int m) {
            data.reserve(m);
            next.reserve(m);
        }

        size_t size() const {return std::size(head);}
        size_t nodes() const {return std::size(data);}

        std::vector<int> head, next;
        std::vector<datatype> data;
    };
}

#line 5 "cp-algo/graph/base.hpp"
#include <ranges>
#line 7 "cp-algo/graph/base.hpp"
namespace cp_algo::graph {
    using edge_index = int;
    enum type {directed = 0, undirected = 1};
    template<type _undirected, edge_type edge_t = edge_base>
    struct graph {
        static constexpr bool undirected = _undirected;
        graph(int n, int v0 = 0): v0(v0), adj(n) {}

        void add_edge(node_index u, edge_t e) {
            adj.push(u, (edge_index)size(edges));
            edges.push_back(e);
            if constexpr (undirected) {
                adj.push(e.to, (edge_index)size(edges));
            }
            edges.push_back(e.backedge(u));
        }
        void read_edges(node_index m) {
            adj.reserve(m);
            for(edge_index i = 0; i < m; i++) {
                auto [u, e] = edge_t::read(v0);
                add_edge(u, e);
            }
        }
        void call_adjacent(node_index v, auto &&callback, auto &&terminate) const {
            for(int sv = adj.head[v]; sv && !terminate(); sv = adj.next[sv]) {
                callback(adj.data[sv]);
            }
        }
        void call_adjacent(node_index v, auto &&callback) const {
            call_adjacent(v, callback, [](){return false;});
        }
        void call_edges(auto &&callback) const {
            for(edge_index e: edges_view()) {
                callback(e);
            }
        }
        auto nodes_view() const {
            return std::views::iota(0, n());
        }
        auto edges_view() const {
            return std::views::iota(0, 2 * m()) | std::views::stride(2);
        }
        auto const& incidence_lists() const {return adj;}
        edge_t const& edge(edge_index e) const {return edges[e];}
        node_index n() const {return (node_index)adj.size();}
        edge_index m() const {return (edge_index)size(edges) / 2;}
    private:
        node_index v0;
        std::vector<edge_t> edges;
        structures::stack_union<edge_index> adj;
    };
}

#line 6 "cp-algo/graph/cycle.hpp"
namespace cp_algo::graph {
    std::vector<int> find_cycle(auto const& g) {
        std::vector<char> state(g.n());
        std::vector<int> cycle;
        auto dfs = [&](auto &&self, int v, int pe) -> bool {
            state[v] = 1;
            bool found = false;
            g.call_adjacent(v, [&](int e) {
                if(e / 2 != pe / 2) {
                    int u = g.edge(e).to;
                    if(state[u] == 0) {
                        if(self(self, u, e)) {
                            if(g.edge(cycle[0]).to != g.edge(cycle.back() ^ 1).to) {
                                cycle.push_back(e);
                            }
                            found = true;
                        }
                    } else if(state[u] == 1) {
                        cycle = {e};
                        found = true;
                    }
                }
            }, [&found](){return found;});
            state[v] = 2;
            return found;
        };
        for(int i: g.nodes_view()) {
            if(!state[i] && dfs(dfs, i, -2)) {
                break;
            }
        }
        std::ranges::reverse(cycle);
        return cycle;
    }
}

#line 7 "verify/graph/cycle_directed.test.cpp"

using namespace std;
using namespace cp_algo::graph;

void solve() {
    int n, m;
    cin >> n >> m;
    graph<directed> g(n);
    g.read_edges(m);
    auto res = find_cycle(g);
    if(empty(res)) {
        cout << -1 << "\n";
    } else {
        cout << size(res) << "\n";
        for(auto it: res) {cout << it / 2 << '\n';}
    }
}

signed main() {
    //freopen("input.txt", "r", stdin);
    ios::sync_with_stdio(0);
    cin.tie(0);
    int t = 1;
    while(t--) {
        solve();
    }
}

Test cases

Env	Name	Status	Elapsed	Memory
g++	example_00	AC	6 ms	6 MB
g++	example_01	AC	5 ms	6 MB
g++	example_02	AC	5 ms	6 MB
g++	long_cycle_00	AC	85 ms	61 MB
g++	long_cycle_01	AC	79 ms	61 MB
g++	random_00	AC	21 ms	22 MB
g++	random_01	AC	36 ms	21 MB
g++	random_02	AC	18 ms	19 MB
g++	random_03	AC	10 ms	8 MB
g++	random_04	AC	15 ms	9 MB
g++	random_05	AC	21 ms	19 MB
g++	random_06	AC	28 ms	14 MB
g++	random_07	AC	7 ms	6 MB
g++	random_08	AC	18 ms	17 MB
g++	random_09	AC	12 ms	12 MB
g++	random_dag_00	AC	37 ms	20 MB
g++	random_dag_01	AC	40 ms	23 MB
g++	random_dag_02	AC	27 ms	19 MB
g++	random_dag_03	AC	10 ms	8 MB
g++	random_dag_04	AC	14 ms	9 MB
g++	random_dag_05	AC	36 ms	19 MB
g++	random_dag_06	AC	27 ms	14 MB
g++	random_dag_07	AC	7 ms	6 MB
g++	random_dag_08	AC	31 ms	17 MB
g++	random_dag_09	AC	20 ms	11 MB
g++	random_dag_dense_00	AC	24 ms	17 MB
g++	random_dag_dense_01	AC	27 ms	16 MB
g++	random_dag_dense_02	AC	24 ms	18 MB
g++	random_dag_dense_03	AC	27 ms	17 MB
g++	random_dag_dense_04	AC	28 ms	20 MB
g++	random_dense_00	AC	17 ms	17 MB
g++	random_dense_01	AC	19 ms	17 MB
g++	random_dense_02	AC	17 ms	18 MB
g++	random_dense_03	AC	19 ms	17 MB
g++	random_dense_04	AC	19 ms	20 MB

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