使用 PHP 创建具有另一个自然数数组的所有排列的数组

Question

我用 $my_array = range(1,3) 创建了一个数组，我想创建一个数组，其中包含这个数组的所有排列 (1,2,3 1,3,2 2,1 ,3 ..)。

范围函数中的第二个数字可以更改（可以是 4、5、7、50 而不是 3）。

Answer 1

来自Christer's blog o' fun 的代码：

function permute($str) {
    /* If we only have a single character, return it */
    if (strlen($str) < 2) {
        return array($str);
    }

    /* Initialize the return value */
    $permutations = array();

    /* Copy the string except for the first character */
    $tail = substr($str, 1);

    /* Loop through the permutations of the substring created above */
    foreach (permute($tail) as $permutation) {
        /* Get the length of the current permutation */
        $length = strlen($permutation);

        /* Loop through the permutation and insert the first character of the original
        string between the two parts and store it in the result array */
        for ($i = 0; $i <= $length; $i++) {
            $permutations[] = substr($permutation, 0, $i) . $str[0] . substr($permutation, $i);
        }
    }

    /* Return the result */
    return $permutations;
}

$array_of_natural_numbers = range(1, 5);
$string_of_natural_numbers = implode("",$array_of_natural_numbers);
$permutations = permute($string_of_natural_numbers);