Php recursion to get all possibilities of strings

Question

Here is my code to get all possibilities:

$seq[1] = \'d\';
$seq[2] = \'f\';
$seq[3] = \'w\';
$seq[4] = \'s\';

for($i = 1; $i < 5; $i++)
{
    $s[\'length         


        

Answer 1

One algorithm is here,

function getCombinations($base,$n){

$baselen = count($base);
if($baselen == 0){
    return;
}
    if($n == 1){
        $return = array();
        foreach($base as $b){
            $return[] = array($b);
        }
        return $return;
    }else{
        //get one level lower combinations
        $oneLevelLower = getCombinations($base,$n-1);

        //for every one level lower combinations add one element to them that the last element of a combination is preceeded by the element which follows it in base array if there is none, does not add
        $newCombs = array();

        foreach($oneLevelLower as $oll){

            $lastEl = $oll[$n-2];
            $found = false;
            foreach($base as  $key => $b){
                if($b == $lastEl){
                    $found = true;
                    continue;
                    //last element found

                }
                if($found == true){
                        //add to combinations with last element
                        if($key < $baselen){

                            $tmp = $oll;
                            $newCombination = array_slice($tmp,0);
                            $newCombination[]=$b;
                            $newCombs[] = array_slice($newCombination,0);
                        }

                }
            }

        }

    }

    return $newCombs;


}

I know it is not efficent in any way, but using in small sets should not be a problem

first base parameter is an array containing elements to be considered when generating combinations.

for simple usage and output:

var_dump(getCombinations(array("a","b","c","d"),2));

and output is

array
  0 => 
    array
      0 => string 'a' (length=1)
      1 => string 'b' (length=1)
  1 => 
    array
      0 => string 'a' (length=1)
      1 => string 'c' (length=1)
  2 => 
    array
      0 => string 'a' (length=1)
      1 => string 'd' (length=1)
  3 => 
    array
      0 => string 'b' (length=1)
      1 => string 'c' (length=1)
  4 => 
    array
      0 => string 'b' (length=1)
      1 => string 'd' (length=1)
  5 => 
    array
      0 => string 'c' (length=1)
      1 => string 'd' (length=1)

To list all subsets of an array, using this combinations algorithm just execute

$base =array("a","b","c","d");

for($i = 1; $i<=4 ;$i++){
    $comb = getCombinations($base,$i);

    foreach($comb as $c){
        echo implode(",",$c)."
";
    }

}

And output is

a
b
c
d
a,b
a,c
a,d
b,c
b,d
c,d
a,b,c
a,b,d
a,c,d
b,c,d
a,b,c,d