int V, group_cnt;

vector<vector<int> > adj, radj;

vector<int> group_num, vis;

stack<int> stk;

// V = number of vertices

SCC(int V): V(V), group_cnt(0), group_num(V), vis(V), adj(V), radj(V) {}

// Call this to add an edge (0-based)

void add_edge(int v1, int v2) {

adj[v1].push_back(v2);

radj[v2].push_back(v1);

}

void fill_forward(int x) {

vis[x] = true;

for (int i = 0; i < adj[x].size(); i++) {

if (!vis[adj[x][i]]) {

fill_forward(adj[x][i]);

}

}

stk.push(x);

}

void fill_backward(int x) {

vis[x] = false;

group_num[x] = group_cnt;

for (int i = 0; i < radj[x].size(); i++) {

if (vis[radj[x][i]]) {

fill_backward(radj[x][i]);

}

}

}

// Returns number of strongly connected components.

// After this is called, group_num contains component assignments (0-based)

int get_scc() {

for (int i = 0; i < V; i++) {

if (!vis[i]) fill_forward(i);

}

group_cnt = 0;

while (!stk.empty()) {

if (vis[stk.top()]) {

fill_backward(stk.top());

group_cnt++;

}

stk.pop();

}

return group_cnt;

}