【java】约瑟夫环

有n个人围成一个圈，顺序排号。从第一个人开始报数（从1到3报数），凡报到3的人退出圈子，问最后留下的是第几号哪位？

import java.util.Scanner;
public class Test4 {
    public static void main(String[] args) {

        Scanner s = new Scanner(System.in);
		System.out.println("请输入人数");
        int n = s.nextInt();
        boolean[] arr = new boolean[n];

        for (int i = 0; i < arr.length; i++) {
            arr[i] = true;
        } //数组赋值都是true

        int leftCount = n;
        int countNum = 0;
        int index = 0;
        while (leftCount > 1) {
            if (arr[index] == true) {
                countNum++;
                if (countNum == 3) {
                    countNum = 0;
                    arr[index] = false;
                    leftCount--;
                }
            }
            index++;
            if (index == n) {
                index = 0;
            }
        }
        for (int i = 0; i < n; i++) {
            if (arr[i] == true) {
                System.out.println("原排在第" + (i + 1) + "位的人留下了");
            }
        }
    }
}