30万员工抽奖

30万个员工，其工卡号码分别是1~30万，抽10万个员工发奖品。有一个随机数生成函数rand()能够生成(0~65535]的整数，请写一个公平的抽奖程序，输出这10万个员工的工卡号码

利用rand5生成rand7算法的原理

import java.util.*;
public class Main {
    private static final int NUM_EMPLOYEES = 300000;
    private static final int NUM_WINNERS = 100000;
    private static final int MAX_RAND = 65535;

    public static void main(String[] args) {
        Set<Integer> winners = fairLottery();
        System.out.println("Number of winners: " + winners.size());
        System.out.println("Winners: " + winners);
    }

    public static Set<Integer> fairLottery() {
        Set<Integer> winners = new HashSet<>();
        Random random = new Random();

        while (winners.size() < NUM_WINNERS) {
            int randomNumber = generateEmployeeNumber(random);
            winners.add(randomNumber);  // 利用 HashSet 自动去重
        }

        return winners;
    }

    // 生成 [1, 300000] 范围的随机数
    public static int generateEmployeeNumber(Random random) {
        while (true) {
            int part1 = rand(random);  // 生成 [1, 65535]
            int part2 = rand(random);  // 生成 [1, 65535]

            // 合成一个更大的随机数
            long largeRand = (long) (part1 - 1) * MAX_RAND + part2;

            // 映射到 [1, 300000] 范围
            if (largeRand <= (long) NUM_EMPLOYEES * MAX_RAND) {
                return (int) ((largeRand - 1) % NUM_EMPLOYEES + 1);
            }
        }
    }

    // 模拟 rand() 函数，返回 [1, 65535] 之间的随机整数
    public static int rand(Random random) {
        return random.nextInt(MAX_RAND) + 1;
    }
}