PHP 实现微信红包拆分算法

<?php 
/** 
 * 红包分配算法 
 * 
 * example 
 *      $coupon = new Coupon(200, 5); 
 *      $res = $coupon->handle(); 
 *      print_r($res); 
 * 
 * @author Flc <2018-04-06 20:09:53> 
 * @see http://flc.ren | http://flc.io | https://github.com/flc1125 
 */ 
class Coupon 
{ 
    /** 
     * 红包金额 
     * 
     * @var float 
     */ 
    protected $amount; 
 
    /** 
     * 红包个数 
     * 
     * @var int 
     */ 
    protected $num; 
 
    /** 
     * 领取的红包最小金额 
     * 
     * @var float 
     */ 
    protected $coupon_min; 
 
    /** 
     * 红包分配结果 
     * 
     * @var array 
     */ 
    protected $items = []; 
 
    /** 
     * 初始化 
     * 
     * @param float $amount     红包金额（单位：元）最多保留2位小数 
     * @param int   $num        红包个数 
     * @param float $coupon_min 每个至少领取的红包金额 
     */ 
    public function __construct($amount, $num = 1, $coupon_min = 0.01) 
    { 
        $this->amount = $amount; 
        $this->num = $num; 
        $this->coupon_min = $coupon_min; 
    } 
 
    /** 
     * 处理返回 
     * 
     * @return array 
     */ 
    public function handle() 
    { 
        // A. 验证 
        if ($this->amount < $validAmount = $this->coupon_min * $this->num) { 
            throw new Exception('红包总金额必须≥'.$validAmount.'元'); 
        } 
 
        // B. 分配红包 
        $this->apportion(); 
 
        return [ 
            'items' => $this->items, 
        ]; 
    } 
 
    /** 
     * 分配红包 
     */ 
    protected function apportion() 
    { 
        $num = $this->num;  // 剩余可分配的红包个数 
        $amount = $this->amount;  //剩余可领取的红包金额 
 
        while ($num >= 1) { 
            // 剩余一个的时候，直接取剩余红包 
            if ($num == 1) { 
                $coupon_amount = $this->decimal_number($amount); 
            } else { 
                $avg_amount = $this->decimal_number($amount / $num);  // 剩余的红包的平均金额 
 
                $coupon_amount = $this->decimal_number( 
                    $this->calcCouponAmount($avg_amount, $amount, $num) 
                ); 
            } 
 
            $this->items[] = $coupon_amount; // 追加分配 
 
            $amount -= $coupon_amount; 
            --$num; 
        } 
 
        shuffle($this->items);  //随机打乱 
    } 
 
    /** 
     * 计算分配的红包金额 
     * 
     * @param float $avg_amount 每次计算的平均金额 
     * @param float $amount     剩余可领取金额 
     * @param int   $num        剩余可领取的红包个数 
     * 
     * @return float 
     */ 
    protected function calcCouponAmount($avg_amount, $amount, $num) 
    { 
        // 如果平均金额小于等于最低金额，则直接返回最低金额 
        if ($avg_amount <= $this->coupon_min) { 
            return $this->coupon_min; 
        } 
 
        // 浮动计算 
        $coupon_amount = $this->decimal_number($avg_amount * (1 + $this->apportionRandRatio())); 
 
        // 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->coupon_min 
            || $coupon_amount > $this->calcCouponAmountMax($amount, $num) 
        ) { 
            return $this->calcCouponAmount($avg_amount, $amount, $num); 
        } 
 
        return $coupon_amount; 
    } 
 
    /** 
     * 计算分配的红包金额-可领取的最大金额 
     * 
     * @param float $amount 
     * @param int   $num 
     */ 
    protected function calcCouponAmountMax($amount, $num) 
    { 
        return $this->coupon_min + $amount - $num * $this->coupon_min; 
    } 
 
    /** 
     * 红包金额浮动比例 
     */ 
    protected function apportionRandRatio() 
    { 
        // 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) { 
            return rand(-70, 70) / 100; // 上下幅度70% 
        } 
 
        return rand(-30, 30) / 100; // 其他情况，上下浮动30%； 
    } 
 
    /** 
     * 格式化金额，保留2位 
     * 
     * @param float $amount 
     * 
     * @return float 
     */ 
    protected function decimal_number($amount) 
    { 
        return sprintf('%01.2f', round($amount, 2)); 
    } 
} 
 
// 例子 
$coupon = new Coupon(200, 5, 30); 
$res = $coupon->handle(); 
print_r($res);