# Strongly Connected Component – Tarjan Algorithm

```#include<bits/stdc++.h>
#define ll long long

struct Tarjan // find all strongly connected components of a directed graph
{
// NOTE:
//      vertex-index can be either 0-BASED or 1-BASED
//      edge is ONE-WAY
//      return all Strongly-Connected-Components with length >= 2

int n; // number of vertice
int *num;
int *low;
int *visited;
int cnt;
vector< vector<int> > sccs;
stack<int> stk;

void init(int n_) {
n = n_;

num = new int[n+1];
low = new int[n+1];
visited = new int[n+1];
}

void addEdge(int u, int v) {
}

void dfs_scc(int u) {
num[u] = low[u] = ++cnt;
stk.push(u);

for (int v : adj[u]) {
if (!visited[v]) {
if (num[v] < 0) {
dfs_scc(v);
low[u] = min(low[u], low[v]);
}
else {
low[u] = min(low[u], num[v]);
}
}
}

if (num[u] == low[u]) {

vector<int> scc;

while (true) {
int top = stk.top();
stk.pop();
scc.push_back(top);
visited[top] = 1;

if (top == u)
break;
}

sccs.push_back(scc);
}

}

vector< vector<int> >findSCC() {

sccs.clear();
while(!stk.empty()) stk.pop();
cnt = 0;
for (int i = 0; i <= n; ++i) {
num[i] = -1;
low[i] = -1;
visited[i] = 0;
}

for (int i = 0; i <= n; ++i)
if (!visited[i])
dfs_scc(i);

return sccs;
}

};
```