/**
* 日期 奖品 权重 库存
* 3.1 1元 5000 5000
* 3.1 2元 1000 1000
* 3.1 3元 500 500
* 3.1 5元 100 100
* 3.1 iphone6s 1 1
* 3.1 未中奖 59409 59409
**/
//奖品库存
//未中奖：假设设定抽10次中一次, 未中奖权重 = 抽检概率导数奖品数-奖品数 = 106601-6601 = 59409
$awardStockMap = ["1元"=>5000,"2元"=>1000,"3元"=>500,"5元"=>100,"iphone"=>1, "未中奖"=>59409];
$awardWeightMap = $awardStockMap;//奖品权重，此处默认为库存
asort($awardWeightMap);
$userNum = 30000;//日活用户数
$drawNum = $userNum * 3;//每天抽奖次数 = 日活数*抽奖次数
$dailyWinCountMap = [];
//模拟每次抽奖
for ($j = 0; $j<$drawNum; $j++) {
//排除掉库存为0的商品
foreach ($awardStockMap as $key => $stock) {
if ($stock == 0) {
unset($awardWeightMap[$key]);
}
}
//获取总权重
$totalWeight = array_sum($awardWeightMap);
//生成一个随机数
$randNum = mt_rand(0, $totalWeight - 1);
$prev = 0;
$chooseAward = "";
//组成区间 0-1 1-101 101-601 601-1601 1601-6601 6601-66010 做比较
foreach ($awardWeightMap as $key => $weight) {
if ($randNum >= $prev && $randNum < ($prev + $weight)) {
$chooseAward = $key;
break;
}
$prev += $weight;
}
//记录每天中奖
if (isset($dailyWinCountMap[$chooseAward])) {
$dailyWinCountMap[$chooseAward]++;
} else {
$dailyWinCountMap[$chooseAward] = 1;
}
//未中奖不用减库存
if ($chooseAward != "未中奖") {
//减库存，记录空库存
//中奖后 会减库存 但假如库存只剩1个了 有10个用户同时落入一元区间 如何避免1-10=-9的情况
//update award_stock set stock = stock - 1 where award_id = ? and stock > 0;
if ((--$awardStockMap[$chooseAward])==0) {
printf("奖品：%s 库存为空<br />", $chooseAward);
}
}
}
//因为生成的随机数可能相同，在“未中奖”不会减库存的情况下，会存在iphone一直都是1/59409的概率
//所以在超低概率的奖品中，会出现抽不中的情况
echo "每日各奖品中奖计数：";
foreach ($dailyWinCountMap as $key => $value) {
echo $key.":".$value." ";
}