在PHP中查找数组元素的所有可能的唯一组合[重复]

Question

This question already has an answer here:

• Finding the subsets of an array in PHP 4 answers

I’m aware of several questions covering this topic (e.g. here), but none of them (at least from what I found) do what I need.

Say I have an array of 3 elements [1, 2, 3]. I need to find all the possible unique combinations (so excluding permutations, like here), including the ones of repeating elements. So the result should be:

[1]
[2]
[3]
[1, 1]
[1, 2]
[1, 3]
[2, 2]
[2, 3]
[3, 3]
[1, 1, 1]
[1, 1, 2]
[1, 1, 3]
[1, 2, 2]
[1, 2, 3]
[1, 3, 3]
[2, 2, 2]
[2, 2, 3]
[2, 3, 3]
[3, 3, 3]

Excluding subsets like [3, 2, 1] or [2, 1, 3], that are the same thing as [1, 2, 3].

How can I achieve this?

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Answer 1

Fast solution using recursion, probably not the best way to do it, but it gets the job done.

<?php

$arr = array(1,2,3);
$result = array();

function combinations($arr, $level, &$result, $curr=array()) {
    for($i = 0; $i < count($arr); $i++) {
        $new = array_merge($curr, array($arr[$i]));
        if($level == 1) {
            sort($new);
            if (!in_array($new, $result)) {
                $result[] = $new;          
            }
        } else {
            combinations($arr, $level - 1, $result, $new);
        }
    }
}
for ($i = 0; $i<count($arr); $i++) {
    combinations($arr, $i+1, $result);
}

// TEST
foreach ($result as $arr) {
    echo join(" ", $arr) . '<br>';
}

?>