detect_cycle_undirected_graph.cpp

//{ Driver Code Starts
#include <bits/stdc++.h>
using namespace std;

// } Driver Code Ends
class Solution {
  private:
   bool detect(int src,vector<int> adj[],int vis[]){
        queue<pair<int,int>>q;
        vis[src]=1;
         q.push({src,-1});
         while(!q.empty()){
             int node=q.front().first;
             int parent=q.front().second;
             q.pop();
             for(auto adjNode:adj[node]){
                 if(!vis[adjNode]){
                     vis[adjNode]=1;
                     q.push({adjNode,node});
                 }
                 else{
                     if(parent !=adjNode)return true;
                 }
             }
             
         }
         return false;
   }
  public:
    // Function to detect cycle in an undirected graph.
    bool isCycle(int V, vector<int> adj[]) {
        int vis[V]={0};
        for(int i=0;i<V;i++){
            if(!vis[i]){
                if(detect(i,adj,vis))return true;
            }
        }
        return false;
        
        
    }
};

//{ Driver Code Starts.
int main() {
    int tc;
    cin >> tc;
    while (tc--) {
        int V, E;
        cin >> V >> E;
        vector<int> adj[V];
        for (int i = 0; i < E; i++) {
            int u, v;
            cin >> u >> v;
            adj[u].push_back(v);
            adj[v].push_back(u);
        }
        Solution obj;
        bool ans = obj.isCycle(V, adj);
        if (ans)
            cout << "1\n";
        else
            cout << "0\n";
    }
    return 0;
}
// } Driver Code Ends