Note: This will work perfectly for this kind of array, where we have array of strings, it does not work for nested array.

Try this code snippet here

<?php
ini_set('display_errors', 1);
$data  = array("a","b","c","e","r","t","x","s","b","a","b","c"); 
$string=  implode("", $data);//converting array to string.
for($x=strlen($string)-1;$x>=0;$x--)
{
    //matching substring from the end of string.
    if(preg_match("/".substr($string, 0,$x)."$/",$string)==true)
    {
        $string= substr($string, 0,$x);
        break;
    }
}
$result=str_split($string);
print_r($result);

I hope this code will work:

 <?php 
   $Input  = array('a','b','c','e','r','t','x','s','b','a','b','c'); 
    $len=count($Input);
    $j=$len-1;
    $count=0;
    $s=0;
    $k=$n=0;
    $a[$len/2];
    for($i=0;$i<$len;$i++)
    {
        if($Input[$i]!=$Input[$j]){
            $j--;
            $i--;
        }
        if($Input[$i]==$Input[$j]){
            $count++;
            $a[$n]=$Input[$j];
            $n++;
            if($k==$j)
            {
                $s++;
                break;
            }
            $k=$j;

            if($j!=$len-1)
                $j++;
            else
                break;
        }
    }
    if($s!=0)
        echo "sequence not present";
    else
        {
            echo "<br>sequence present <br>";
            $len2=count($a);
            for($p=0;$p<$len2;$p++)
                echo" ".$a[$p];
        }

    ?>

sunny, I've got a good one for you!

Method:

$found=false;                                              // declare default outcome
for($x=1,$max=sizeof($data); $x<=$max; ++$x){              // this allows "overlap"
    if(array_slice($data,0,$x)===array_slice($data,-$x)){  // compare start to end
        $found=true;                                       // declare a match has occurred
    }elseif($found){                                       // this iteration is no match
        --$x;                                              // rewind to successful match
        break;
    }
}
var_export($found?array_slice($data,0,$x):"No match");      // output the result

Inputs & Outputs:

$data=['a','b','c','e','r','t','x','s','b','a','b','c'];  // ['a','b','c']
$data=['n','o','p','e'];                                  // No Match
$data=['r','a','c','e','c','a','r'];                      // ['r']
$data=['a','a','b','a','a'];                              // ['a','a']

Explanation:

It is more efficient and advisable to avoid regex based solutions whenever possible. Furthermore, I managed to write a solution that keeps the input in array form (avoiding unnecessary conversions).

array_slice() is the clear hero of this answer. As $x increments, the two array_slice() calls stay in sync allowing a simple conditional comparison.

$max is set to iterate the whole array and welcomes the possibility of "overlap" within the array. If you don't want any chance of "overlap", you can use $max=floor(sizeof($data)/2)

After a match is found, as soon as there is a non-match, the loop will break and the correct output will be displayed.

Question extension...

Palindromic Matching -- You can easily adjust my above method to match mirrored sequences by adding array_reverse().

Method:

$found=false;
for($x=1,$max=sizeof($data); $x<=$max; ++$x){
    if(array_slice($data,0,$x)===array_reverse(array_slice($data,-$x))){  // only change
        $found=true;
    }elseif($found){
        --$x;
        break;
    }
}
var_export($found?array_slice($data,0,$x):"No match");

Inputs & Outputs:

$data=['a','b','c','e','r','t','x','s','b','a','b','c'];    // No Match
$data=['n','o','p','e'];                                    // No Match
$data=['r','a','c','e','c','a','r'];                        // ['r','a','c','e','c','a','r']
$data=['a','a','b','a','a'];                                // ['a','a','b','a','a']