PHP採取一切組合

Question

我看到這個algorithm that will take numbers or words and find all possible combinations

而且我使用它，但它不會返回所有的「真實」的組合。

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"; 
    } 
?> 

，並返回：

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

但這些並不都是真正的組合，所有真正的組合，包括這些太：

cat cat 
dog dog 
fish fish 

而這正是我需要，獲得所有真實組合的方法：

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

Answer 1

OK，這裏是你的代碼（順便說一句，感謝張貼這樣一個有趣和具有挑戰性的問題 - 至少對我來說... :-)） - 使用遞歸對所有可能的排列（由N）給出一個數組元件）

代碼：

<?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); 

?> 

輸出：

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：通過permutations($words,2)，你就可以得到正是你想要的東西......

Answer 2

您當前的代碼給你排列，只需添加重複：

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

什麼問題？