Encode/compress sequence of repeating integers

Question

I have very long integer sequences that look like this (arbitrary length!):

0000000001110002220033333

Now I need some algorithm to convert

Answer 1

It is called Run Length Encoding

Basic encoder in PHP:

function numStringToRle($s){
    $rle = '';
    $count = 1;
    $len = strlen($s);
    for ( $i = 0; $i < $len; $i++ ){
        if ( $i != $len && $s[$i] == $s[$i+1] ){
            $count++;                
        }else{
          $rle .= chr($s[$i] + 97).$count;    
          $count = 1;
        }
    }
    return $rle;
}

Be warned it will preform badly issues with a string like

 123456789123456789

If you were going to be handling a string that may have a lot of individual single characters you would be better to add some complexity and not write the length of the run if the length of the run is 1.

//change
$rle .= chr($s[$i] + 97).$count;    

//to
$rle .= chr($s[$i] + 97).( $count == 1 ? '' : $count );   

//or
$rle .= chr($s[$i] + 97)
if ( $count != 1 ){
    $rle .= $count;
}