detectcycle_undirect_bfs

bool bfshelper(int root,vector<int> adj[],vector<bool>& visited)
    {
        visited[root]=true;
        queue<pair<int,int>> pendingnodes;
        pendingnodes.push(make_pair(root,-1));
        while(!pendingnodes.empty())
        {
            pair<int,int> front=pendingnodes.front();
            pendingnodes.pop();
            for(int i=0;i<adj[front.first].size();i++)
            {
                int neighbour=adj[front.first][i];
                if(front.second==neighbour) continue;
                if(visited[neighbour]) return true;
                visited[neighbour]=true;
                pendingnodes.push(make_pair(neighbour,front.first));
            }
        }
        return false;
    }
    bool isCycle(int V, vector<int> adj[]) {
        vector<bool> visited(V,false);
        for(int i=0;i<V;i++)
        {
            if(!visited[i] && bfshelper(i,adj,visited)) return true;
        }
        return false;
    }