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    <p><strong>Solution</strong></p> <pre><code>function combinationsByLenth($arr, $len) { $combinations = []; $select = array_fill(0, $len, 0); $selectCount = count($select); $arrCount = count($arr); $possibleCombinations = pow($arrCount, $selectCount); while ($possibleCombinations-- &gt; 0) { $combination = ''; foreach ($select as $index) { $combination .= $arr[$index]; } $combinations[] = $combination; for ($i = $selectCount - 1; $i &gt;= 0; $i--) { if ($select[$i] !== ($arrCount - 1)) { $select[$i]++; break; } else { $select[$i] = 0; } } } return $combinations; } function combinationsByMinMax($arr, $min, $max) { $combinations = []; for ($i = $min; $i &lt;= $max; $i++) { $combinations = array_merge($combinations, combinationsByLenth($arr, $i)); } return $combinations; } print_r(combinationsByMinMax($arr, 1, 5)); </code></pre> <p><strong>Output</strong></p> <pre><code>Array ( [0] =&gt; a [1] =&gt; b [2] =&gt; c [3] =&gt; 1 [4] =&gt; 2 [5] =&gt; 3 [6] =&gt; aa [7] =&gt; ab [8] =&gt; ac [9] =&gt; a1 ... [9320] =&gt; 3332c [9321] =&gt; 33321 [9322] =&gt; 33322 [9323] =&gt; 33323 [9324] =&gt; 3333a [9325] =&gt; 3333b [9326] =&gt; 3333c [9327] =&gt; 33331 [9328] =&gt; 33332 [9329] =&gt; 33333 ) </code></pre> <p><strong>Rationale</strong></p> <ul> <li>Avoid recursive solutions for this type of problem in PHP (note, I like recursion in languages optimized to handle it better) to avoid stack issues as the length grows.</li> <li>Break the function up into two separate functions, one that implements min and max length, and one that gets the possible combinations for a specific length to promote reuse and clarity.</li> <li>Limit function calls within the 2 functions as much as possible to enhance performance (this algorithm gets heavy fast!)</li> </ul> <p><strong>How I Developed This Solution</strong></p> <p>I started out with a function that handled the specific case of combinations of length 5, refactored to generalize the algorithm, refactored to generalize the algorithm, etc. I've put up a quick gist so you can see the iterations to get to this working version as a case study of how to approach building this type of algorithm:</p> <p><a href="https://gist.github.com/AdamJonR/5278480" rel="nofollow">https://gist.github.com/AdamJonR/5278480</a></p>
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    1. POAlgorithm to get all possible string combinations from array up to certain length
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    1. COHow does this works?
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    2. CO@Phpdna, in short, the combinationsByMinMax() function cycles through each possible length of the combination and passes in the array and the length to the combinationsByLenth() function, which just cycles through the array elements to pull in all of the possible combinations for that length. For example, if the array is [a,b,c,d] and the length is 3 for the combinationsByLength() function, it would create outputs aaa, aab, aac, etc. Let me know if you would like greater detail. And, sorry for the typo in the function name (missing the 'g'.)
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    3. COI need an algorithm with all unique combinations. This thing is all permutations.
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