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php实现抽奖概率

2026-02-16 13:35:05PHP

PHP实现抽奖概率的方法

方法一：使用数组和随机数

创建一个包含奖项和对应概率的数组，使用随机数进行抽奖判断。

php实现抽奖概率

$prizes = [
    ['name' => '一等奖', 'probability' => 0.01],
    ['name' => '二等奖', 'probability' => 0.05],
    ['name' => '三等奖', 'probability' => 0.1],
    ['name' => '谢谢参与', 'probability' => 0.84]
];

function drawLottery($prizes) {
    $rand = mt_rand(1, 10000) / 10000;
    $currentProbability = 0;

    foreach ($prizes as $prize) {
        $currentProbability += $prize['probability'];
        if ($rand <= $currentProbability) {
            return $prize['name'];
        }
    }
    return end($prizes)['name'];
}

echo drawLottery($prizes);

方法二：使用权重分配

为每个奖项分配权重值，计算总权重后随机选择。

php实现抽奖概率

$prizes = [
    ['name' => 'iPhone', 'weight' => 1],
    ['name' => 'iPad', 'weight' => 5],
    ['name' => '优惠券', 'weight' => 20],
    ['name' => '谢谢参与', 'weight' => 74]
];

function weightedDraw($prizes) {
    $totalWeight = array_sum(array_column($prizes, 'weight'));
    $rand = mt_rand(1, $totalWeight);
    $currentWeight = 0;

    foreach ($prizes as $prize) {
        $currentWeight += $prize['weight'];
        if ($rand <= $currentWeight) {
            return $prize['name'];
        }
    }
}

echo weightedDraw($prizes);

方法三：概率递减算法

适用于需要保证某些奖项必中或限制次数的场景。

$prizes = [
    ['name' => '特等奖', 'initial_prob' => 0.01, 'remaining' => 1],
    ['name' => '一等奖', 'initial_prob' => 0.05, 'remaining' => 5],
    ['name' => '二等奖', 'initial_prob' => 0.1, 'remaining' => 10],
    ['name' => '参与奖', 'initial_prob' => 1, 'remaining' => 1000]
];

function decreasingProbabilityDraw($prizes) {
    $totalRemaining = array_sum(array_column($prizes, 'remaining'));
    if ($totalRemaining <= 0) return '奖品已发完';

    $adjustedProbs = [];
    foreach ($prizes as $prize) {
        if ($prize['remaining'] > 0) {
            $adjustedProbs[] = [
                'name' => $prize['name'],
                'prob' => $prize['initial_prob'] * ($prize['remaining'] / $totalRemaining)
            ];
        }
    }

    $rand = mt_rand(1, 10000) / 10000;
    $currentProb = 0;

    foreach ($adjustedProbs as $prize) {
        $currentProb += $prize['prob'];
        if ($rand <= $currentProb) {
            return $prize['name'];
        }
    }

    return '谢谢参与';
}

echo decreasingProbabilityDraw($prizes);

方法四：使用概率别名算法

对于大量奖品的高效抽样方法，适合复杂概率分布场景。

class AliasMethod {
    private $n;
    private $prob;
    private $alias;

    public function __construct($weights) {
        $this->n = count($weights);
        $this->prob = array_fill(0, $this->n, 0);
        $this->alias = array_fill(0, $this->n, 0);

        $sum = array_sum($weights);
        $scaled = array_map(function($w) use ($sum) {
            return $w * $this->n / $sum;
        }, $weights);

        $small = [];
        $large = [];

        foreach ($scaled as $i => $w) {
            if ($w < 1) {
                $small[] = $i;
            } else {
                $large[] = $i;
            }
        }

        while (!empty($small) && !empty($large)) {
            $l = array_pop($small);
            $g = array_pop($large);

            $this->prob[$l] = $scaled[$l];
            $this->alias[$l] = $g;

            $scaled[$g] = ($scaled[$g] + $scaled[$l]) - 1;

            if ($scaled[$g] < 1) {
                $small[] = $g;
            } else {
                $large[] = $g;
            }
        }

        foreach ($large as $i) {
            $this->prob[$i] = 1;
        }

        foreach ($small as $i) {
            $this->prob[$i] = 1;
        }
    }

    public function draw() {
        $i = mt_rand(0, $this->n - 1);
        if (mt_rand() / mt_getrandmax() <= $this->prob[$i]) {
            return $i;
        } else {
            return $this->alias[$i];
        }
    }
}

$weights = [1, 2, 3, 4]; // 各奖项权重
$sampler = new AliasMethod($weights);
$result = $sampler->draw(); // 返回抽中的索引