gistfile1.php

<?php
function findset($s, $l){
    $len = count($s);
    $outAry = array();
    $ptrs = array();
    for($i=0;$i<$l;$i++){
        $ptrs[] = $i;
    }
    $i=0;
	$curPtr = $l-1;
    while($ptrs[0] < $len - $l + 1){
        foreach($ptrs as $j => $pt){
            $outAry[$i][$j] = $s[$pt];
        }
		if($ptrs[$curPtr]+1 < $len-$curPtr){
			$ptrs[$curPtr]++;
		}else{
			// go back to find where new pointer can start again
			for($j=$curPtr-1;$j>=0;$j--){
				if($ptrs[$j] < $len - 1 - $j){
					$curPtr = $j;
					break;
				}
			}
			$ptrs[$curPtr]++;
			$curPtr++;
			for($j=$curPtr;$j<$l;$j++){
				$ptrs[$j]=$ptrs[$j-1]+1;
			}
		}
        $i++;
    };
    return $outAry;
}