тупое говно тупого говна на 96

    #include <iostream>
    #include <vector>

    using namespace std;

    vector<vector<int>> g;
    vector<bool> visited;
    vector<int> cycle;

    int ans = 0;

    void svaznost_chek(int v, int prev)
    {
        if (ans || cycle[v])
            return;

        cycle[v] = -1;
        for (auto v_i : g[v])
        {
            if (cycle[v_i] < 0 && v_i != prev)
            {
                ans = 1;
                return;
            }
            svaznost_chek(v_i, v);
        }

        cycle[v] = 1;
    }


    int main()
    {
        int n, m;
        cin >> n >> m;

        visited.resize(n, false);
        g.resize(n);
        cycle.resize(n, 0);

        for (int i = 0; i < m; ++i)
        {
            int a, b;
            cin >> a >> b;
            a--;
            b--;

            g[a].push_back(b);
            g[b].push_back(a);
        }

        // проверка на связность
        svaznost_chek(0, 0);
        if (!ans)
        {
            for (int j = 0; j < n; ++j)
            {
                if (cycle[j] == 0)
                {
                    cout << "NO";
                    break;
                }
            }
            cout << "YES";
        }
        else
            cout << "NO";

        return 0;
    }