public class Main {    public static void main(String[] args) {        // 构造从start到end的序列：        final int start = 10;        final int end = 20;        List<Integer> list = new ArrayList<>();        for (int i = start; i <= end; i++) {            list.add(i);        }        // 洗牌算法suffle可以随机交换List中的元素位置:        Collections.shuffle(list);        // 随机删除List中的一个元素:        int removed = list.remove((int) (Math.random() * list.size()));        //int removed = list.remove((10));        int found = findMissingNumber(start, end, list);        System.out.println(list.toString());        System.out.println("missing number: " + found);        System.out.println(removed == found ? "测试成功" : "测试失败");    }    /**     * TODO: 找出从start到end的缺失的数字并返回     */    static int findMissingNumber(int start, int end, List<Integer> list) {        Collections.sort(list);        for (int i = 0; i < list.size(); i++) {            if ((i + 1 < list.size()) && list.get(i + 1) - list.get(i) == 2) {                return list.get(i) + 1;            }            if ((i + 1 == list.size())) {                return list.get(i) + 1;            }        }        return 0;    }}

应该是想引出排序,偷懒了,直接使用工具类了