graph - Biconnected Component

/*
Output The biconnected Component of an undirected graph
0 - base indexing
use init first. adde then.
bc[i] = # of i biconnected component.
*/

#include <bits/stdc++.h>
#define FO(i,a,b) for (int i = (a); i < (b); i++)
#define sz(v) int(v.size())

using namespace std;
struct bcc {
    vector<vector<int> > u;
    vector<int> bc, lo, ind,SZ;
    vector<vector<int> > G;
    int T, m, n;

    void init(int n_) {
        n = n_; m = 0; T = 0;
        u.clear(); u.resize(n);
        G.clear(); G.resize(n);
        bc.assign(n,-1);
        lo.assign(n,-1);
        SZ.assign(n,0);
        ind.assign(n,-1);

    }

    void adde(int i, int j) {
        u[i].push_back(j);
        u[j].push_back(i);
    }

    vector<int> stk;
    void go(int i, int p) {
        ind[i] = lo[i] = ++T;
        stk.push_back(i);

        for (int j : u[i]) if (j != p) {
            if (ind[j] == -1) {
                go(j, i);
                lo[i] = min(lo[i],lo[j]);
            } else {
                lo[i] = min(lo[i],ind[j]);
            }
        } else p = -1;

        if (ind[i] == lo[i]) {
            int t;
            do {
                t = stk.back(); stk.pop_back();
                bc[t] = m;
            } while (t != i);
            m++;
        }
    }

    void dobcc() {
        FO(i,0,n) if (ind[i] == -1) go(i,-1);
    }
};