Find first and last matching sequence in array php - php

Question

I have a array to find sequence of alphabets and then fetch last and first combination. I am trying something like this.
$aarr = ['x','y','z','t','m','n','x','y','z'];
$str = implode('',$aarr);
$all_subset = powerSet($aarr);
foreach ($all_subset as $set) {
$sre_temp = implode('', $set);
$tru = hasOrderedCharactersForward($sre_temp);
if($tru){
echo $sre_temp.'<br>';
}
}
function powerSet($array) {
// add the empty set
$results = array(array());
foreach ($array as $element) {
foreach ($results as $combination) {
$results[] = array_merge(array($element), $combination);
}
}
return $results;
}
function hasOrderedCharactersForward($str, $i = 2) {
$alpha = 'abcdefghijklmnopqrstuvwxyz';
$len = strlen($str);
for($j=0; $j <= $len - $i; $j++){
if(strrpos($alpha, substr($str, $j, $i)) !== false){
return true;
}
}
return false;
}
I think powerSet() is not working like i think. Even it should show 'xyz' as combination but its not;

Answer 1

Have a look at this and make use of it if it fits your needs.
$aarr = ['x','y','z','t','m','n','x','y','z'];
$subsets = [];
$i=0;
#here we merge all chars to sub-sequence
foreach($aarr as $k=>$v){
$subsets[$i][]=$v;
if(isset($aarr[$k+1]) && ord($v)+1!==ord($aarr[$k+1])){
$i++;
}
}
$subsets = array_map(function($a){ return implode('',$a);},$subsets);
print_r($subsets);
Result:
Array ( [0] => xyz [1] => t [2] => mn [3] => xyz )
Getting the first and last value:
#get first
$first=null;
$i=0;
do{
if(strlen($subsets[$i])>1){#find sequence
$first = $subsets[$i];
}
$i++;
}while(!$first && isset($subsets[$i]));
#get last
$last=null;
$i=count($subsets)-1;
do{
if(strlen($subsets[$i])>1){#find sequence
$last = $subsets[$i];
}
$i--;
}while(!$last && isset($subsets[$i]));
print "$first, $last";
Result:
xyz, xyz