我试图推断出一个算法产生的特定的大小类似的函数，它接受字符数组和大小，它的参数和返回的组合阵列中所有可能的组合。

I am trying to deduce an algorithm which generates all possible combinations of a specific size something like a function which accepts an array of chars and size as its parameter and return an array of combinations.

例： 让我们说我们有一组字符的： 集合A = {A，B，C}

Example: Let say we have a set of chars: Set A = {A,B,C}

一）2号的所有可能的组合：（3 ^ 2 = 9）

a) All possible combinations of size 2: (3^2 = 9)

AA, AB, AC
BA, BB, BC
CA, CB, CC

二）规模3所有可能的组合：（3 ^ 3 = 27）

b) All possible combinations of size 3: (3^3 = 27)

AAA, AAB, AAC,
ABA, ABB, ACC,
CAA, BAA, BAC,
.... ad so on total combinations = 27

请注意，一对大小可大于pouplation的总大小。例如果设置有3个字符那么我们还可以创建一个大小为4的组合。

Please note that the pair size can be greater than total size of pouplation. Ex. if set contains 3 characters then we can also create combination of size 4.

修改： 还要注意的是，这是从排列不同。在置换我们不能有重复字符例如AA不能来，如果我们使用置换算法。在统计学中，它被称为采样。

EDIT: Also note that this is different from permutation. In permutation we cannot have repeating characters for example AA cannot come if we use permutation algorithm. In statistics it is known as sampling.

推荐答案

我会用递归函数。这里的（工作）的例子有意见。希望这对你的作品！

I would use a recursive function. Here's a (working) example with comments. Hope this works for you!

function sampling($chars, $size, $combinations = array()) {

    # if it's the first iteration, the first set 
    # of combinations is the same as the set of characters
    if (empty($combinations)) {
        $combinations = $chars;
    }

    # we're done if we're at size 1
    if ($size == 1) {
        return $combinations;
    }

    # initialise array to put new values in
    $new_combinations = array();

    # loop through existing combinations and character set to create strings
    foreach ($combinations as $combination) {
        foreach ($chars as $char) {
            $new_combinations[] = $combination . $char;
        }
    }

    # call same function again for the next iteration
    return sampling($chars, $size - 1, $new_combinations);

}

// example
$chars = array('a', 'b', 'c');
$output = sampling($chars, 2);
var_dump($output);
/*
array(9) {
  [0]=>
  string(2) "aa"
  [1]=>
  string(2) "ab"
  [2]=>
  string(2) "ac"
  [3]=>
  string(2) "ba"
  [4]=>
  string(2) "bb"
  [5]=>
  string(2) "bc"
  [6]=>
  string(2) "ca"
  [7]=>
  string(2) "cb"
  [8]=>
  string(2) "cc"
}
*/