DetectCycleUndirectedBfs.java

import java.util.*;
public class Solution {
    
    public static String cycleDetection(int[][] edges, int n, int m) {
        ArrayList<TreeSet<Integer>> adjList = new ArrayList<>();
        for(int i=0;i<=n;i++){
            adjList.add(new TreeSet<Integer>());
        }
        
        for(int j=0;j<edges.length;j++){
            adjList.get(edges[j][0]).add(edges[j][1]);
            adjList.get(edges[j][1]).add(edges[j][0]);
        }
        
        boolean[] visited = new boolean[n+1];
        for(int i=1;i<=n;i++){
            if(!visited[i] && dfs(-1,i,visited,adjList)){
                return "Yes";
            }
        }
        
        return "No";
    }
    public static boolean dfs(int prev,int node,boolean[] visited,ArrayList<TreeSet<Integer>> adjList){
        visited[node] = true;
        for(Integer x : adjList.get(node)){
            if(!visited[x]){
                if(dfs(node,x,visited,adjList)){
                    return true;
                }
            }
            else if(x!=prev)
                return true;
        }
        return false;
    }
}