判断二分图

int istwo(int u)
{
    queue<int> E;
    mem(vis, -1);
    E.push(u);
    vis[u] = 1;
    while(!E.empty())
    {
        u = E.front(); E.pop();
        for(int i=0; i<G[u].size(); i++)
        {
            int v = G[u][i];
            if(vis[v] == -1)
            {
                if(vis[u] == 1) vis[v] = 0;
                else vis[v] = 1;
                E.push(v);
            }
            else if(vis[v] == vis[u])
                return 0;
        }
    }
    return 1;
}

int main()
{
    istwo(1);
}