How to implement counting sorting code in PHP

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Release: 2023-04-03 14:14:01
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This article introduces to you the code on how to implement counting sorting in PHP. It has certain reference value. Friends in need can refer to it. I hope it will be helpful to you.

/**
 * 计数排序: 桶排序的一种
 */
$arr = [5,69,4,32,14,8,74,95,23,56,41,5,31,63];
// include 'data.php';
$length = count($arr);
$maxValue = $arr[0];

// 找出数组中的最大值
for ($i=1; $i < $length; $i++) {
    if ($arr[$i] > $maxValue) {
        $maxValue = $arr[$i];
    }
}
/**
 * 定长数组, 键会自动排序, PHP数组是hash表的实现,
 * 如果这里用普通的数组, 键不会自动排序, 不存在的键也不会自动填充null
 */
$frequency = new SplFixedArray($maxValue + 1);

/**
 * 统计arr中, 值出现的频次
 */
for ($i=0; $i < $length; $i++) {
    if(empty($frequency[$arr[$i]]))
        $frequency[$arr[$i]] = 0;
    $frequency[$arr[$i]] += 1;
}

// 清空$arr
$arr = [];
// 遍历frequency, 如果其元素有值, 那么将键push到arr中
for ($i=0; $i < count($frequency); $i++) {
    if (!empty($frequency[$i])) {
        for ($j=0; $j < $frequency[$i]; $j++) {
            $arr[] = $i;
        }
    }
}

print_r($arr);
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