约瑟夫环

import java.util.ArrayList;

public class Test {
    public static void main(String[] args) {
        
    }
    
    public static int fun() {
        ArrayList<Integer> al = new ArrayList<>();
        for (int i = 1; i <= 500; i++) {
            al.add(i);
        }
        int count = 1;
        for (int i = 0; al.size() != 1; i++) {
            if (i == al.size()) {
                i = 0;
            }
            if (count % 3 == 0) {
                al.remove(i--);
            }
            count++;
        }
        return al.get(0);
    }
}