按概率抽奖算法

RandomCoupon.java

    public static void main(String[] args) {
        int all = 1000000;
        Map<Integer, Integer> results = Maps.newHashMap();
        for (int i = 0; i < all; i++) {
            int id = chanceSelect(couponProbability);
            if (!results.containsKey(id)) {
                results.put(id, 0);
            }
            results.put(id, results.get(id) + 1);
        }
        for (int i = 91; i<=100; i++) {
            System.out.println(i + ": "+ results.get(i));
        }

    }

    private static Map<Integer, Integer> couponProbability = ImmutableMap.<Integer, Integer>builder()
        .put(91, 400)
        .put(92, 200)
        .put(93, 150)
        .put(94, 80)
        .put(95, 55)
        .put(96, 40)
        .put(97, 30)
        .put(98, 20)
        .put(99, 15)
        .put(100, 10)
        .build();

    /**
     * 概率选择
     * @param keyChanceMap key为唯一标识，value为该标识的概率，是去掉%的数字
     * @return 被选中的key。未选中返回0
     */
    public static int chanceSelect(Map<Integer, Integer> keyChanceMap) {
        if (keyChanceMap == null || keyChanceMap.size() == 0) {
            return 0;
        }

        Integer sum = 0;
        for (Integer value : keyChanceMap.values()) {
            sum += value;
        }
        // 从1开始
        int rand = new Random().nextInt(sum) + 1;

        for (Map.Entry<Integer, Integer> entry : keyChanceMap.entrySet()) {
            rand -= entry.getValue();
            // 选中
            if(rand <= 0) {
                return entry.getKey();
            }
        }

        return 0;
    }