PHP采用所有组合

我看到这个algorithm that will take numbers or words and find all possible combinations

我正在使用它,但它不会返回所有“真正的”组合.

PHP：

<?php
    require_once 'Math/Combinatorics.php';
    $words = array('cat', 'dog', 'fish');
    $combinatorics = new Math_Combinatorics;
    foreach($combinatorics->permutations($words, 2) as $p) {
        echo join(' ', $p), "\n"; 
    }
?>

它返回：

cat dog
dog cat
cat fish
fish cat
dog fish
fish dog

但这些都不是真正的组合,所有真正的组合也包括这些：

cat cat
dog dog
fish fish

这就是我需要的,获得所有真实组合的方法：

cat dog
dog cat
cat fish
fish cat
dog fish
fish dog
cat cat
dog dog
fish fish

解决方法:

好的,这是你的代码(顺便说一句,感谢发布这样一个有趣且具有挑战性的问题 – 至少对我来说…… :-)) – 在给定元素数组的情况下对所有可能的排列(由N)使用递归

代码：

<?php

function permutations($arr,$n)
{
     $res = array();

     foreach ($arr as $w)
     {
           if ($n==1) $res[] = $w;
           else
           {
                 $perms = permutations($arr,$n-1);

                 foreach ($perms as $p)
                 {
                      $res[] = $w." ".$p;
                 } 
           }
     }

     return $res;
}

// Your array
$words = array('cat','dog','fish');

// Get permutation by groups of 3 elements
$pe = permutations($words,3);

// Print it out
print_r($pe);

?>

输出：

Array
(
    [0] => cat cat cat
    [1] => cat cat dog
    [2] => cat cat fish
    [3] => cat dog cat
    [4] => cat dog dog
    [5] => cat dog fish
    [6] => cat fish cat
    [7] => cat fish dog
    [8] => cat fish fish
    [9] => dog cat cat
    [10] => dog cat dog
    [11] => dog cat fish
    [12] => dog dog cat
    [13] => dog dog dog
    [14] => dog dog fish
    [15] => dog fish cat
    [16] => dog fish dog
    [17] => dog fish fish
    [18] => fish cat cat
    [19] => fish cat dog
    [20] => fish cat fish
    [21] => fish dog cat
    [22] => fish dog dog
    [23] => fish dog fish
    [24] => fish fish cat
    [25] => fish fish dog
    [26] => fish fish fish
)

提示：通过排列($words,2),你将能够得到你想要的……

标签：discrete-mathematics,php,algorithm,combinations,combinatorics
来源： https://codeday.me/bug/20190925/1815955.html