This documentation is automatically generated by online-judge-tools/verification-helper
#define PROBLEM "https://judge.yosupo.jp/problem/scc"
#include "atcoder/scc.hpp"
#include <iostream>
int main() {
int n, m;
std::cin >> n >> m;
atcoder::scc_graph g(n);
for (int i = 0; i < m; i++) {
int u, v;
std::cin >> u >> v;
g.add_edge(u, v);
}
auto scc = g.scc();
std::cout << scc.size() << '\n';
for (auto &v : scc) {
int k = v.size();
std::cout << k << ' ';
for (int i = 0; i < k; i++) {
std::cout << v[i] << " \n"[i == k - 1];
}
}
}
#line 1 "test/library-checker/scc.test.cpp"
#define PROBLEM "https://judge.yosupo.jp/problem/scc"
#line 1 "atcoder/scc.hpp"
#include <algorithm>
#include <cassert>
#include <vector>
#line 1 "atcoder/internal_scc.hpp"
#line 5 "atcoder/internal_scc.hpp"
#include <utility>
#line 7 "atcoder/internal_scc.hpp"
#line 1 "atcoder/internal_csr.hpp"
#line 7 "atcoder/internal_csr.hpp"
namespace atcoder {
namespace internal {
template <class E> struct csr {
std::vector<int> start;
std::vector<E> elist;
explicit csr(int n, const std::vector<std::pair<int, E>>& edges)
: start(n + 1), elist(edges.size()) {
for (auto e : edges) {
start[e.first + 1]++;
}
for (int i = 1; i <= n; i++) {
start[i] += start[i - 1];
}
auto counter = start;
for (auto e : edges) {
elist[counter[e.first]++] = e.second;
}
}
};
} // namespace internal
} // namespace atcoder
#line 9 "atcoder/internal_scc.hpp"
namespace atcoder {
namespace internal {
// Reference:
// R. Tarjan,
// Depth-First Search and Linear Graph Algorithms
struct scc_graph {
public:
explicit scc_graph(int n) : _n(n) {}
int num_vertices() { return _n; }
void add_edge(int from, int to) { edges.push_back({from, {to}}); }
// @return pair of (# of scc, scc id)
std::pair<int, std::vector<int>> scc_ids() {
auto g = csr<edge>(_n, edges);
int now_ord = 0, group_num = 0;
std::vector<int> visited, low(_n), ord(_n, -1), ids(_n);
visited.reserve(_n);
auto dfs = [&](auto self, int v) -> void {
low[v] = ord[v] = now_ord++;
visited.push_back(v);
for (int i = g.start[v]; i < g.start[v + 1]; i++) {
auto to = g.elist[i].to;
if (ord[to] == -1) {
self(self, to);
low[v] = std::min(low[v], low[to]);
} else {
low[v] = std::min(low[v], ord[to]);
}
}
if (low[v] == ord[v]) {
while (true) {
int u = visited.back();
visited.pop_back();
ord[u] = _n;
ids[u] = group_num;
if (u == v) break;
}
group_num++;
}
};
for (int i = 0; i < _n; i++) {
if (ord[i] == -1) dfs(dfs, i);
}
for (auto& x : ids) {
x = group_num - 1 - x;
}
return {group_num, ids};
}
std::vector<std::vector<int>> scc() {
auto ids = scc_ids();
int group_num = ids.first;
std::vector<int> counts(group_num);
for (auto x : ids.second) counts[x]++;
std::vector<std::vector<int>> groups(ids.first);
for (int i = 0; i < group_num; i++) {
groups[i].reserve(counts[i]);
}
for (int i = 0; i < _n; i++) {
groups[ids.second[i]].push_back(i);
}
return groups;
}
private:
int _n;
struct edge {
int to;
};
std::vector<std::pair<int, edge>> edges;
};
} // namespace internal
} // namespace atcoder
#line 9 "atcoder/scc.hpp"
namespace atcoder {
struct scc_graph {
public:
scc_graph() : internal(0) {}
explicit scc_graph(int n) : internal(n) {}
void add_edge(int from, int to) {
int n = internal.num_vertices();
assert(0 <= from && from < n);
assert(0 <= to && to < n);
internal.add_edge(from, to);
}
std::vector<std::vector<int>> scc() { return internal.scc(); }
private:
internal::scc_graph internal;
};
} // namespace atcoder
#line 3 "test/library-checker/scc.test.cpp"
#include <iostream>
int main() {
int n, m;
std::cin >> n >> m;
atcoder::scc_graph g(n);
for (int i = 0; i < m; i++) {
int u, v;
std::cin >> u >> v;
g.add_edge(u, v);
}
auto scc = g.scc();
std::cout << scc.size() << '\n';
for (auto &v : scc) {
int k = v.size();
std::cout << k << ' ';
for (int i = 0; i < k; i++) {
std::cout << v[i] << " \n"[i == k - 1];
}
}
}