如何生成字符串的排列，但没有重复和不同的长度？

Question

I am looking for a php algorithm or just pseudo code to get all permutations of a string, but without repeat of the characters and the length of generated string can variate from 1 to the maximum length of the input. Example:

input: 1 2 3

possible combinations:

1

1 2 / ( it is the same as 2 1, so that must not be calculated)

1 3

1 2 3

2

2 3

3

Answer 1

Here you go :

function pc_array_power_set($array) {
    // initialize by adding the empty set
    $results = array(array());

    foreach ($array as $element)
        foreach ($results as $combination)
            array_push($results, array_merge(array($element), $combination));

   return $results;

}

From PHP Cookbook