MP3光标位置（算法）

  /**
     * MP3光标位置
     * 1 、 获取当前歌曲位置  获取当前光标在4首歌哪个位置  获取总页数长度
     * 2 、 计算光标前后 有几个数
     * 3 、 把前后的数拼接
     *
     * @param args
     */
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        while (scanner.hasNext()) {
            Integer number = scanner.nextInt();
            String upDown = scanner.next();
 
            int pageSize = 4;
            if (number < pageSize) {
                pageSize = number;
            }
 
            // 歌曲位置
            int index = 1;
            // 光标位置
            int pageIndex = 1;
            for (int i = 0; i < upDown.length(); i++) {
                if (upDown.charAt(i) == 'U') {
                    if (index == 1) {
                        index = number;
                        pageIndex = pageSize;
                    } else {
                        index--;
                        if (pageIndex != 1) {
                            pageIndex--;
                        }
                    }
                } else if (upDown.charAt(i) == 'D') {
                    if (index == number) {
                        index = 1;
                        pageIndex = 1;
                    } else {
                        index++;
                        if (pageIndex != pageSize) {
                            pageIndex++;
                        }
                    }
                }
            }
 
            int next = pageSize - pageIndex;
            int pre = pageSize - 1 - next;
 
            String page = "";
            for (int i = pre; i > 0; i--) {
                page += (index - i) + " ";
            }
            page += index + " ";
            for (int i = 1; i <= next; i++) {
                page += (index + i) + " ";
            }
            page = page.substring(0,page.length()-1);
            System.out.println(page);
            System.out.println(index);
        }
 
    }