Strong connectivity
https://cp-algorithms.com/graph/strongly-connected-components.html
Kosaraju’s
// credit from https://github.com/Autoratch/practice
#include <bits/stdc++.h>
using namespace std;
const int N = 1e5 + 1;
int n, m;
vector<int> adj[N], rev[N];
stack<int> st;
bool visited[N];
void dfs(int u) {
if (visited[u])
return;
visited[u] = true;
for (int v : adj[u])
dfs(v);
st.push(u);
}
void scc(int u) {
if (visited[u])
return;
visited[u] = true;
cout << u << ' ';
for (int v : rev[u])
scc(v);
}
int main() {
ios_base::sync_with_stdio(0);
cin.tie(0);
cin >> n >> m;
for (int i = 0; i < m; i++) {
int a, b;
cin >> a >> b;
adj[a].push_back(b);
rev[b].push_back(a);
}
for (int i = 1; i <= n; i++)
if (!visited[i])
dfs(i);
memset(visited, 0, sizeof visited);
while (!st.empty()) {
int u = st.top();
st.pop();
if (visited[u])
continue;
scc(u);
cout << '\n';
}
}