bool dfs(int u, int col)
{
    color[v] = 1;
    bool flag = false;
    for (int i = 0; i < s[v].size(); i++){
        int u = s[v][i];
        if (color[u] == 0)
            dfs(u);
        if (color[u] == 1)
            flag = true;
    }
    color[v] = 2;
    return flag;
}