抽奖算法总结

// 分别为一、二、三、四等将的奖品数量，最后一个为未中奖的数量。
private static final Integer[] lotteryList = {5, 10, 20, 40, 100};

private int getSum() {
int sum = 0;
for (int v : lotteryList) {
sum += v;
}
return sum;
}

private int getLotteryLevel() {
Random random = new Random(System.nanoTime());
int sum = getSum();
for (int i = 0; i < lotteryList.length; ++i) {
int randNum = Math.abs(random.nextInt()) % sum;
if (randNum <= lotteryList[i]) {
return i;
} else {
sum -= lotteryList[i];
}
}
return -1;
}

//另一种抽奖算法，用于公司抽奖，即总参与人数与奖品数固定。
private static final int lotteryNum = 75;
private static final int total = 175;
private static Set<Integer> lotterySet = new HashSet<Integer>();
static {
for (int i=1; i <= lotteryNum; ++i) {
lotterySet.add(total*i/lotteryNum);
}
}
private int getLotteryNum2() {
Random rand = new Random(System.nanoTime());
int randNum = Math.abs(rand.nextInt()) % total;
if (lotterySet.contains(randNum)) {
return randNum*lotteryNum/total;
}
return -1;
}