PHP采取一切组合

Question

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

而且我使用它，但它不会返回所有的“真实”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"; 
    } 
?> 

，并返回：

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

但这些并不都是真正的组合，所有真正的组合，包括这些太：

cat cat 
dog dog 
fish fish 

而这正是我需要，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 

Answer 1

OK，这里是你的代码（顺便说一句，感谢张贴这样一个有趣和具有挑战性的问题 - 至少对我来说... :-)） - 使用递归对所有可能的排列（由N）给出一个数组元件）

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permutations($words,2)，你就可以得到正是你想要的东西......

Answer 2

您当前的代码给你排列，只需添加重复：

foreach($words as $w) { 
    echo "$w $w\n";  
} 

什么问题？