java 从1到1亿随机 找出未出现的数字

public class Test {public static void main(String args[]) {BitSet used = new BitSet();Random rand = new Random(47);for (int i = 1; i < 100000001; i++) {used.set(rand.nextInt(100000000) + 1); // set bit for char}List<Integer> list = new ArrayList<Integer>();for (int i = 1; i < 100000001; i++) {if (!used.get(i))list.add(i);}System.out.println(list.size());}}