Tarjan's strongly connected component algorithm

TarjanSCC.cpp

/*
Below code is function which returns number of strongly connected components.

https://www.youtube.com/watch?v=TyWtx7q2D7Y
https://www.tutorialspoint.com/Tarjan-s-Algorithm-for-Strongly-Connected-Components
*/

int id;
int ans;

void dfs(int x, 
        vector < int > adj[], 
        vector < bool > &visited, 
        vector < int > &ids, 
        vector < int > &low, 
        stack < int > &s, 
        vector < bool > &in_stack) {
    
    visited[x] = true;
    in_stack[x] = true;
    s.push(x);
    ids[x] = low[x] = id++;
    
    for (auto i : adj[x]) {
        if (!visited[i]) {
            dfs(i, adj, visited, ids, low, s, in_stack);
            low[x] = min(low[x], low[i]);
        } else if (in_stack[i]) {
            low[x] = min(low[x], low[i]);
        }
    }
    
    if (ids[x] == low[x]) {
        while (s.top() != x) {
            in_stack[s.top()] = false;
            s.pop();
        }
        in_stack[s.top()] = false;
        s.pop();
        ans++;
    }
}

int TarjanSCC(int V, vector<int> adj[]) {
    ans = 0;
    id = 0;
    vector < int > ids(V, 0);
    vector < int > low(V, 0);
    vector < bool > visited(V, false);
    vector < bool > in_stack(V, false);
    stack < int > s;
    
    for (int i = 0; i < V; i++) {
        if (!visited[i])
            dfs(i, adj, visited, ids, low, s, in_stack);
    }
    
    return ans;
}