分享实现PHP红包算法的思路（附开发代码）

根据很多需求的使用场景，如发红包、砍价类需求，这两个功能都有一个同样的特点，如下：

<?php

/**
 * 发送红包
 * Class sandRed
 */
class sandRed
{
    #红包金额
    protected $amount;
    #红包个数
    protected $num;
    #领取的红包最小金额
    protected $minAmount;
    #红包分配结果
    protected $amountArr = [];

    public function __construct($amount, $num = 1, $minAmount = 1)
    {
        $this->amount = $amount;
        $this->num = $num;
        $this->minAmount = $minAmount;
    }

    /**
     * 处理返回
     * @return array
     * @throws Exception
     */
    public function handle()
    {
        # 验证
        if ($this->amount < $validAmount = $this->minAmount * $this->num) {
            throw new Exception('红包总金额必须≥'.$validAmount.'元');
        }
        # 分配红包
        $this->allot();
        return $this->amountArr;
    }

    /**
     * 分配红包
     */
    protected function allot()
    {
        # 剩余可分配的红包个数
        $num = $this->num;

        # 剩余可领取的红包金额
        $amount = $this->amount;
        while ($num >= 1) {
            if ($num == 1) {
                # 剩余一个的时候，直接取剩余红包
                $coupon_amount = $this->formattingAmount($amount);
            } else {

                # 平均金额
                $avgAmount = $this->formattingAmount($amount / $num);

                # 分配金额
                $countAllotAmount = $this->countAllotAmount($avgAmount, $amount, $num);

                # 剩余的红包的平均金额
                $coupon_amount = $this->formattingAmount($countAllotAmount);
            }
            # 追加分配金额
            $this->amountArr[] = $coupon_amount;

            # 计算剩余金额
            $amount -= $coupon_amount;

            $num--;
        }
        # 随机打乱
        // shuffle($this->amountArr);
    }

    /**
     * 计算分配的红包金额
     * @param float $avgAmount 每次计算的平均金额
     * @param float $amount 剩余可领取金额
     * @param int $num 剩余可领取的红包个数
     * @return float
     */
    protected function countAllotAmount($avgAmount, $amount, $num)
    {
        # 如果平均金额小于等于最低金额，则直接返回最低金额
        if ($avgAmount <= $this->minAmount) {
            return $this->minAmount;
        }
        # 浮动比率
        $floatingRate = $this->floatingRate();

        # 分配金额
        $allotAmount = $avgAmount * (1 + $floatingRate);

        # 浮动计算
        $coupon_amount = $this->formattingAmount($allotAmount);

        # 如果低于最低金额或超过可领取的最大金额，则重新获取
        if ($coupon_amount < $this->minAmount || $coupon_amount > $this->canReceiveMaxAmount($amount, $num)) {
            return $this->countAllotAmount($avgAmount, $amount, $num);
        }
        return $coupon_amount;
    }

    /**
     * 计算分配的红包金额-可领取的最大金额
     * @param $amount
     * @param $num
     * @return float|int
     */
    protected function canReceiveMaxAmount($amount, $num)
    {
        return $this->minAmount + $amount - $num * $this->minAmount;
    }

    /**
     * 红包金额浮动比例
     * @return float|int
     */
    protected function floatingRate()
    {
        # 60%机率获取剩余平均值的大幅度红包（可能正数、可能负数）
        if (rand(1, 100) <= 60) {
            # 上下幅度70%
            return rand(-70, 70) / 100;
        }
        # 其他情况，上下浮动30%；
        return rand(-30, 30) / 100;
    }

    /**
     * 格式化金额，保留2位
     * @param $amount
     * @return string
     */
    protected function formattingAmount($amount)
    {
        return sprintf('%01.2f', round($amount, 2));
    }
}

$amount = 1;

$num = 10;

$minAmount = 0.01;

$red = new sandRed($amount, $num, $minAmount);

$res = $red->handle();
print_r($res);

echo array_sum($res);