php随机红包金额算法

使用方法：

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$coupon = new Coupon(10,8,0.01);
$res = $coupon->handle();
print_r($res['items']);

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打印结果：

Array
(
    [0] => 1.31
    [1] => 1.14
    [2] => 0.81
    [3] => 0.96
    [4] => 1.76
    [5] => 1.31
    [6] => 1.05
    [7] => 1.05
    [8] => 1.54
    [9] => 0.51
    [10] => 0.41
    [11] => 0.44
    [12] => 0.75
    [13] => 0.71
    [14] => 0.91
    [15] => 0.69
    [16] => 1.96
    [17] => 0.85
    [18] => 1.84
)