Believer & non-believer

There are 30 persons, 15 are believers, 15 are non-believers, they plan to travel.
A bus can only carry 15 of them, the rest have to be left behind.
Someone suggests they stand in a circle and count, beginning from him, every time one counts to 9, he has to stay and quite counting.
Finally all the 15 believers will travel, all 15 non-believers have to stay.
The question: how do they stand in the line?
有30个人， 15个信徒， 15个非信徒，他们计划去旅行。但是大巴只能装下15个人，剩下的人没法去，得留下。
有人提议站成一个圆圈，从他起，轮流数数，每个数到9的人就留下，退出圆圈，不再参与数数。
到最后剩下的15个人，发现都是信徒，那么问题是，这30个人是如何站成一个圈的。

import java.util.ArrayList;

public class Believer {

    public static void main(String[] args) {
        ArrayList<Boolean> list = new ArrayList<>();
        for (int i = 1; i <= 30; i ++) {
            list.add(true);
        }

        /*
        true means believer
        false means nonBeliever
         */

        int remaining = 15; // remaining nonBeliever
        int index = 0; // the index of the list, should no be greater than 29
        int count = 0; // the number of the count, when count is 9, someone has to stay
        while (remaining > 0) { // when there are still non-believers
            if (list.get(index)) { // when counts to a non-believer, set to false, so the next round will ignore this element
                count ++;
                if (count == 9) {
                    list.set(index, false); // this is a non-believer
                    remaining --;
                    count = 0;
                }
            }
            index ++;
            if (index == 30) {
                index = 0;
            }
        }
        System.out.println(list);
    }

}

[true, true, true, true, false, false, false, false, false, true, true, false, true, true, true, false, true, false, false, true, true, false, false, false, true, false, false, true, true, false].

def main():
    circle = [True] * 30
    remaining = 15
    count = 0
    index = 0

    while remaining > 0:
        if circle[index]:
            count = count + 1
            if count == 9:
                circle[index] = False
                count = 0
                remaining = remaining - 1
        index = index + 1
        if index == 30:
            index = 0

    print(circle)


if __name__ == "__main__":
    main()

[True, True, True, True, False, False, False, False, False, True, True, False, True, True, True, False, True, False, False, True, True, False, False, False, True, False, False, True, True, False]

Believer & non-believer

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