[그래프/개념] 그래프 사이클 찾기 (방향, 무방향), DFS Cycle java

무방향 그래프에 사이클이 존재하는지의 여부를 확인하는 java 코드입니다.

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.Stack;
import java.util.StringTokenizer;
 
// http://clearpal7.blogspot.kr/2016/10/cycle.html
// 무방향 그래프 -> cycle찾기
public class isCycle {
    static int N, M, T, cnt, flag;
    static ArrayList<Integer> adj[];
    static boolean visited[];
 
    public static void main(String[] args) throws Exception {
        // TODO Auto-generated method stub
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        StringTokenizer st;
        T = Integer.parseInt(br.readLine());
        for(int test_case = 1; test_case <=T; test_case++){
            st = new StringTokenizer(br.readLine());
            N = Integer.parseInt(st.nextToken());
            M = Integer.parseInt(st.nextToken());
            
            adj = new ArrayList[N+1];
            for(int i=1; i<=N; i++){
                adj[i] = new ArrayList<>();
            }
            for(int i=1; i<=M; i++){
                st = new StringTokenizer(br.readLine());
                int u = Integer.parseInt(st.nextToken());
                int v = Integer.parseInt(st.nextToken());
                adj[u].add(v);
                adj[v].add(u);
            }
            visited = new boolean[N+1];
            if(isDfsCycle(1, -1)){
                System.out.println("사이클이다");
            }else{
                System.out.println("사이클 아니다");
            }
        }
    }
 
    private static boolean isDfsCycle(int curr, int parent) {
        visited[curr] = true;
        for(int next : adj[curr]){
            if(!visited[next]){
                if(isDfsCycle(next, curr)){
                    return true;
                }
            }else if(next != parent){
                return true;
            }
        }
        return false;
    }
 
 
}