Detect cycle in an undirected graph(BFS).cpp

      private: 
  bool detect(int src, vector<int> adj[], vector<int>&vis) {
      vis[src] = 1; 
        
      // store <source node, parent node>
      queue<pair<int,int>> q; 
      q.push({src, -1}); 
      while(!q.empty()) {
          int node = q.front().first; 
          int parent = q.front().second; 
          q.pop(); 
          for(auto&x : adj[node]){
              if(!vis[x]) {
                  vis[x] = 1; 
                  q.push({x, node}); 
              }
              else if(parent != x) {
                  return true; 
              }
          }
      }
      return false; 
  }
  public:
    bool isCycle(int V, vector<int> adj[]) {
        vector<int>vis(V,0);
        for(int i = 0;i<V;i++) {
            if(!vis[i]) {
                if(detect(i, adj, vis)) return true; 
            }
        }
        return false; 
    }