Компоненты_вершинной_двусвязности

#include <vector>
#include <algorithm>
#include <iostream>
#include <map>
#include <queue>
using namespace std;

vector <int> tin;
vector <int> up;
vector <bool> was;
vector <vector<int>> gr;
vector <bool> cut_p;
int P = 0;
queue <pair <int, int> > buf;
map < pair <int,int> , int> marker;
int color = 1;
void dfs(int v, int last, int timer) {
    was[v] = true;
    tin[v] = up[v] = timer;
    int child = 0;
    for (int u: gr[v]){

        if (u == last) {

            continue;
        }
        else if (was[u] == true){
            up[v] = min(up[v], tin[u]);
            if (tin[u] < tin[v]){
                buf.push({min(u,v), max(u,v)});
            }
        }
        else if (was[u] == false){
            dfs(u, v, timer + 1);
            up[v] = min(up[v], up[u]);
            if (up[u] >= tin[v]){
                if (!cut_p[v]) P++;
                cut_p[v] = true;
                while (true){
                    pair <int,int> edge = buf.back();
                    buf.pop();
                    marker[{min(u,v), max(u,v)}] = color;
                    if (edge.first == min(v,u) && edge.second ==  max(v,u) ){
                        color++;
                        break;
                    }
                }
            }
            child++;
        }
    }
    if (v == last && child > 1) {
        if (!cut_p[v]) P++;
        cut_p[v] = true;
    }
}

int main()
{
    int n, m;
    cin >> n >> m;
    gr.resize(n);
    cut_p.resize(n, false);
    vector <pair<int,int> > Edges;
    for (int i = 0; i < m; ++i) {
        int a, b;
        cin >> a >> b;
        a--;
        b--;
        gr[a].push_back(b);
        gr[b].push_back(a);
        marker[{min(a,b), max(a,b)}] = -1;
        Edges.push_back({min(a,b), max(a,b)});
    }
    tin.resize(n, -4);
    up.resize(n, 1e9);
    was.resize(n, false);
    for (int i = 0;i<n;++i){
        if (!was[i]) {
            dfs(i, -1, 0);
        }
    }
    /*cout<<"\ntin\n";
    for (int i = 0;i<n;++i){
        cout<<i+1<<": "<<tin[i]<<'\n';
    }cout<<'\n';
    cout<<"up\n";
    for (int i=0;i<n;++i){
        cout<<i+1<<": "<<up[i]<<'\n';
    }cout<<'\n';
    cout <<"amount of cut_points = "<< P<< '\n';
    for (int i= 0;i<n;++i){
        if (cut_p[i]){
            cout<<i+1<<'\n';
        }
    }*/
    was.assign(n, false);
    int cnt = -1;
    for (int i = 0;i<n;++i){
        if (!was[i]){
            cnt++;
            dfs(i, -1, cnt);
        }
    }
    cout<<"\nmarking\n";
    for (auto x: Edges){
        cout<<"("<<x.first + 1<<","<<x.second + 1<<") = "<<marker[x]<<'\n';
    }
    cout<<"DONE\n";
}