PHP采用所有组合

Question

我看到这个算法将采用数字或单词并找到所有可能的组合

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

Answer 1

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...... :-)) - 在给定一系列元素的情况下,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permutations($words,2),你将能够得到你想要的......