shuffle.txt

import java.io.*;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashMap;
import java.util.StringTokenizer;

public class shuffle {
    public static void main(String[] args) throws IOException {
        BufferedReader f = new BufferedReader(new FileReader("shuffle.in"));
        PrintWriter out = new PrintWriter(new BufferedWriter(new FileWriter("shuffle.out")),true);
        int x = Integer.parseInt(f.readLine());
        StringTokenizer st = new StringTokenizer(f.readLine());
        int[] swaps = new int[x];
        for(int i=0; i<x; i++){
            swaps[i]=Integer.parseInt(st.nextToken())-1;
        }
        boolean[] processed = new boolean[x];
        boolean[] inCycle = new boolean[x];
        for(int i=0; i<x; i++){
            if(!processed[i]){
                HashMap<Integer,Integer> map = new HashMap<>();
                ArrayList<Integer> direction = new ArrayList<>();
                int iter=0;
                int current = i;
                boolean cycleFound = false;
                while (!map.containsKey(current)&&!processed[current]){
                    map.put(current,iter);
                    direction.add(current);
                    processed[current]=true;
                    current=swaps[current];
                    iter++;
                    if(map.containsKey(current)){
                        cycleFound=true;
                    }
                }
                if(cycleFound){
                    for(int j = map.get(current); j<iter; j++){
                        inCycle[direction.get(j)]=true;
                    }
                }

            }

        }
        int ans = 0;
        for(int i=0; i<x; i++){
            if(inCycle[i]){
                System.out.println(i);
                ans++;
            }
        }
        out.println(ans);
        out.close();
    }
}