Biconnected Components

stack<pair<int, int> > BCC_stack;

void BCCUtil(vector<int> adj[], int u, bool visited[],
            int disc[], int low[], int& time, int parent)
{

    // Mark the current node as visited
    visited[u] = true;

    // Initialize discovery time and low value
    disc[u] = low[u] = ++time;

    // Go through all vertices adjacent to this
    for (auto v : adj[u]) {
        // If v is not visited yet, then make it a child of u
        // in DFS tree and recur for it
        if (!visited[v]) {
            BCC_stack.push(make_pair(u, v)); // add edge to the stack

            BCCUtil(adj, v, visited, disc, low, time, u, isAP);

            // Check if the subtree rooted with v has
            // a connection to one of the ancestors of u
            low[u] = min(low[u], low[v]);

            // If u is not root and low value of one of
            // its child is more than discovery value of u.
            if (parent != -1 && low[v] >= disc[u]) {
                // pop values from stack until we see the (u, v) edge and those edges are a BCC
                vector<pair<int, int> > current_component;

                pair<int, int> value = BCC_stack.top();
                BCC_stack.pop();
                current_component.push_back(value);
                while (value != make_pair(u, v)) {
                    value = BCC_stack.top();
                    BCC_stack.pop();
                    current_component.push_back(value);
                }
            }

            if (parent == -1) { // we are the root node
                // pop values from stack until we see the (u, v) edge and those edges are a BCC
                vector<pair<int, int> > current_component;

                pair<int, int> value = BCC_stack.top();
                BCC_stack.pop();
                current_component.push_back(value);
                while (value != make_pair(u, v)) {
                    value = BCC_stack.top();
                    BCC_stack.pop();
                    current_component.push_back(value);
                }
            }
        }

        // Update low value of u for parent function calls.
        else if (v != parent)
            low[u] = min(low[u], disc[v]);

    }

}