算法笔记 -- 约瑟夫环问题Java两种写法

// 问题背景： 10人围成圈，从1-3数数，数到3退出，求最后推出的人？

public static void main(String[] args){
    // 约瑟夫环问题
    // 法一：使用单向环连表
    Linked head = initLinked();
    Linked last = doGame(head);
    System.out.println(last.val);

    System.out.println("----------------");

    // 法二：使用数组
    int[][] arr = {{1, 1}, {2, 1}, {3, 1}, {4, 1}, {5, 1}, {6, 1}, {7, 1}, {8, 1}, {9, 1}, {10, 1}};
    System.out.println(doGame(arr));
}

    private static int doGame(int[][] arr) {
        int idx = 1;
        for (;;) {
            if (arr.length == 1) return arr[0][0];
            int retCnt = arr.length;
            for (int i = 0; i < arr.length; i ++) {
                if (idx % 3 == 0) {
                    retCnt --;
                    arr[i][1] = 0;
                    System.out.println(idx + " | " + arr[i][0]);
                }
                idx ++;
            }
            int[][] newArr = new int[retCnt][];
            int newIdx = 0;
            for (int[] a : arr) {
                if (a[1] != 0) {
                    newArr[newIdx ++] = a;
                }
            }
            arr = newArr;
        }
    }

    private static Linked doGame(Linked head) {
        Linked prev = head;
        int idx = 1;
        for (;;) {
            if (prev.next == prev) return prev;
            if (idx % 3 == 0) {
                System.out.println(idx + " | " + head.val);
                Linked next = head.next;
                prev.next = next;
                head.next = null;
                head = next;
            } else {
                prev = head;
                head = head.next;
            }
            idx ++;
        }
    }

    private static Linked initLinked() {
        Linked head = new Linked(1), cur = head;
        for (int i = 2; i < 11; i ++) {
            Linked newCur = new Linked(i);
            cur.next = newCur;
            cur = newCur;
        }
        cur.next = head;
        return head;
    }

    static class Linked {
        int val;
        Linked next;
        public Linked(int val) {
            this.val = val;
        }
    }