1459 : 숫자고르기

import java.util.ArrayList;
import java.util.Scanner;
 
public class Main {
 
    static int n;
    static int arr[] = new int [101];
     
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        Scanner scan = new Scanner(System.in);
        ArrayList<Integer> aList = new ArrayList<Integer>();
         
        int i;
         
        n = scan.nextInt();
         
        for (i = 1; i <= n; i++) {
            arr[i] = scan.nextInt();
        }
         
        for (i = 1; i <= n; i++) {
            if (check(i)) {
                aList.add(i);
            }
        }
         
        System.out.println(aList.size());
        for (int t:aList) {
            System.out.println(t);
        }
         
    }
 
    private static boolean check(int start) {
        // TODO Auto-generated method stub
        int next = arr[start];
         
        int visit[] = new int [101];
         
        visit[start] = 1;
         
        while (visit[next] == 0) {
            visit[next]=1;
            next = arr[next];
        }
        if (next == start) return true;
         
        return false;
    }
 
}

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